Insect winter ecology
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Insect winter ecology describes the
overwinter Overwintering is the process by which some organisms pass through or wait out the winter season, or pass through that period of the year when "winter" conditions (cold or sub-zero temperatures, ice, snow, limited food supplies) make normal activi ...
survival strategies of
insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pairs ...
s, which are in many respects more similar to those of plants than to many other animals, such as mammals and birds. Unlike those animals, which can generate their own heat internally (
endotherm An endotherm (from Greek ἔνδον ''endon'' "within" and θέρμη ''thermē'' "heat") is an organism that maintains its body at a metabolically favorable temperature, largely by the use of heat released by its internal bodily functions inste ...
ic), insects must rely on external sources to provide their heat (
ectotherm An ectotherm (from the Greek () "outside" and () "heat") is an organism in which internal physiological sources of heat are of relatively small or of quite negligible importance in controlling body temperature.Davenport, John. Animal Life a ...
ic). Thus, insects persisting in winter weather must tolerate
freezing Freezing is a phase transition where a liquid turns into a solid when its temperature is lowered below its freezing point. In accordance with the internationally established definition, freezing means the solidification phase change of a liquid o ...
or rely on other mechanisms to avoid freezing. Loss of enzymatic function and eventual freezing due to low temperatures daily threatens the livelihood of these organisms during winter. Not surprisingly, insects have evolved a number of strategies to deal with the rigors of winter temperatures in places where they would otherwise not survive. Two broad strategies for winter survival have evolved within
Insecta Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pairs o ...
as solutions to their inability to generate significant heat
metabolically Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
.
Migration Migration, migratory, or migrate may refer to: Human migration * Human migration, physical movement by humans from one region to another ** International migration, when peoples cross state boundaries and stay in the host state for some minimum le ...
is a complete avoidance of the temperatures that pose a threat. An alternative to migration is weathering the cold temperatures present in its normal habitat. Insect cold tolerance is generally separated into two strategies, freeze avoidance and freeze tolerance.


Migration

See:
Insect migration Insect migration is the seasonal movement of insects, particularly those by species of dragonflies, beetles, butterflies and moths. The distance can vary with species and in most cases, these movements involve large numbers of individuals. In som ...
Migration of insects differs from migration of birds.
Bird migration Bird migration is the regular seasonal movement, often north and south along a flyway, between breeding and wintering grounds. Many species of bird migrate. Migration carries high costs in predation and mortality, including from hunting by ...
is a two-way, round-trip movement of each individual, whereas this is not usually the case with insects. As a consequence of the (typically) short lifespan of insects, adult insects who have completed one leg of the trip may be replaced by a member of the next generation on the return voyage. As a result,
invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...
biologist A biologist is a scientist who conducts research in biology. Biologists are interested in studying life on Earth, whether it is an individual Cell (biology), cell, a multicellular organism, or a Community (ecology), community of Biological inter ...
s redefine migration for this group of organisms in three parts: # A persistent, straight line movement away from the natal area # Distinctive pre- and post-movement behaviors # Re-allocation of energy within the body associated with the movement This definition allows for mass insect movements to be considered as migration. Perhaps the best known insect migration is that of the
monarch butterfly The monarch butterfly or simply monarch (''Danaus plexippus'') is a milkweed butterfly (subfamily Danainae) in the family Nymphalidae. Other common names, depending on region, include milkweed, common tiger, wanderer, and black-veined brown. It ...
. The monarch in
North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
migrates from as far north as
Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
southward to
Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...
and
Southern California Southern California (commonly shortened to SoCal) is a geographic and Cultural area, cultural region that generally comprises the southern portion of the U.S. state of California. It includes the Los Angeles metropolitan area, the second most po ...
annually from about August to October. The population east of the Rocky Mountains overwinters in Michoacán, Mexico, and the western population overwinters in various sites in central coastal California, notably in Pacific Grove and Santa Cruz. The round trip journey is typically around 3,600 km in length. The longest one-way flight on record for monarchs is 3,009 km from
Ontario Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central Ca ...
, Canada to
San Luis Potosí San Luis Potosí (), officially the Free and Sovereign State of San Luis Potosí ( es, Estado Libre y Soberano de San Luis Potosí), is one of the 32 states which compose the Federal Entities of Mexico. It is divided in 58 municipalities and i ...
, Mexico. They use the direction of sunlight and magnetic cues to orient themselves during migration. The monarch requires significant energy to make such a long flight, which is provided by fat reserves. When they reach their overwintering sites, they begin a period of lowered metabolic rate. Nectar from flowers procured at the overwintering site provides energy for the northward migration. To limit their energy use, monarchs congregate in large clusters in order to maintain a suitable temperature. This strategy, similar to huddling in small mammals, makes use of body heat from all the organisms and lowers heat loss. Another common winter migrant insect, found in much of North America, South America, and the
Caribbean The Caribbean (, ) ( es, El Caribe; french: la Caraïbe; ht, Karayib; nl, De Caraïben) is a region of the Americas that consists of the Caribbean Sea, its islands (some surrounded by the Caribbean Sea and some bordering both the Caribbean Se ...
, is the
Green Darner The green darner or common green darner (''Anax junius''), after its resemblance to a darning needle, is a species of dragonfly in the family Aeshnidae. One of the most common and abundant species throughout North America, it also ranges south ...
. Migration patterns in this species are much less studied than those of monarchs. Green darners leave their northern ranges in September and migrate south. Studies have noted a seasonal influx of green darners to southern Florida, which indicates migratory behavior. Little has been done with tracking of the green darner, and reasons for migration are not fully understood since there are both resident and migrant populations. The common cue for migration southward in this species is the onset of winter.


Cold tolerance

Insects that do not migrate from regions with the onset of colder temperatures must devise strategies to either tolerate or avoid lethal freezing of
intracellular This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...
and
extracellular This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...
body fluids. Insects that survive subfreezing temperatures are generally classified as freeze-avoidant or freeze-tolerant. The general strategy adopted by insects differs between the northern hemisphere and the southern hemisphere. In temperate regions of the northern hemisphere where cold temperatures are expected seasonally and are usually for long periods of time, the main strategy is freeze avoidance. In temperate regions of the southern hemisphere, where seasonal cold temperatures are not as extreme or long lasting, freeze tolerance is more common. However, in the Arctic, where freezing occurs seasonally, and for extended periods (>9 months), freeze tolerance also predominates.


Dangers of freezing

Intracellular ice formation usually causes cell death, even in freeze-tolerant species, due to physical stresses exerted as ice crystals expand. Ice formation in extracellular spaces increases the concentration of solutes in the extracellular fluid, resulting in the osmotic flow of water from intracellular spaces to extracellular spaces. Changes in solute concentration and dehydration can cause changes in enzyme activity and lead to the denaturation of proteins. If the temperature continues to decrease, the water that was drawn out of cells will also freeze, causing further cell shrinkage. Excessive cell shrinkage is dangerous because as ice forms outside the cell, the possible shapes that can be assumed by the cells are increasingly limited, causing damaging deformation.Mazur P (1984) Freezing of living cells: mechanisms and implications. ''American Journal of Physiology''. 247:C125–142 Finally, the expansion of ice within vessels and other spaces can cause physical damage to structures and tissues.


Freeze avoidance

Freeze-avoidant insects cannot tolerate internal ice formation, so they avoid freezing by depressing the temperature at which their body fluids freeze. This is done through
supercooling Supercooling, also known as undercooling, is the process of lowering the temperature of a liquid or a gas below its melting point without it becoming a solid. It achieves this in the absence of a seed crystal or nucleus around which a crystal ...
, the process by which a liquid cools below its freezing point without changing phase into a solid. In order for water to freeze, a nucleus must be present upon which an ice crystal can begin to grow. At low temperatures, nuclei may arise spontaneously from clusters of slow-moving water molecules. Alternatively, substances that facilitate the aggregation of water molecules can increase the probability that they will reach the critical size necessary for ice formation. If no source of nucleation is introduced, water can cool down to −48°C without freezing. Therefore, when an insect maintains its body fluids in a supercooled state, there is the risk that spontaneous ice
nucleation In thermodynamics, nucleation is the first step in the formation of either a new thermodynamic phase or structure via self-assembly or self-organization within a substance or mixture. Nucleation is typically defined to be the process that deter ...
will occur. The temperature at which an insect spontaneously freezes is referred to as the supercooling point (SCP). For freeze avoidant insects, the SCP is thought to be equivalent to the lower lethal temperature (LLT) of the organism. The freezing process is usually initiated extracellularly in the gut, tissues, or hemolymph. In order to supercool to lower temperatures, freeze-avoidant insects will remove or inactivate ice-nucleating agents (INAs) such as food particles, dust particles, and bacteria, found in the gut or intracellular compartments of these organisms. Removal of ice-nucleating material from the gut can be achieved by cessation in feeding, clearing the gut, and removing
lipoprotein A lipoprotein is a biochemical assembly whose primary function is to transport hydrophobic lipid (also known as fat) molecules in water, as in blood plasma or other extracellular fluids. They consist of a triglyceride and cholesterol center, sur ...
ice nucleators (LPINs) from the
haemolymph Hemolymph, or haemolymph, is a fluid, analogous to the blood in vertebrates, that circulates in the interior of the arthropod (invertebrate) body, remaining in direct contact with the animal's tissues. It is composed of a fluid plasma in which ...
. Freezing can also be initiated by external contact with ice (inoculative freezing). Thus, some insects avoid freezing by selecting a dry hibernation site in which no ice
nucleation In thermodynamics, nucleation is the first step in the formation of either a new thermodynamic phase or structure via self-assembly or self-organization within a substance or mixture. Nucleation is typically defined to be the process that deter ...
from an external source can occur. Insects may also have a physical barrier such as a wax-coated cuticle that provides protection against external ice across the cuticle. The stage of development at which an insect over-winters varies across species, but can occur at any point of the life cycle (i.e., egg, pupa, larva, and adult). Some species of
Collembola Springtails (Collembola) form the largest of the three lineages of modern hexapods that are no longer considered insects (the other two are the Protura and Diplura). Although the three orders are sometimes grouped together in a class called Ento ...
tolerate extreme cold by the shedding of the mid-gut during
moult In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is the manner in which an animal routinely casts off a part of its body (often, but not always, an outer ...
ing. In addition to physical preparations for winter, many insects also alter their biochemistry and metabolism. For example, some insects synthesize
cryoprotectant A cryoprotectant is a substance used to protect biological tissue from freezing damage (i.e. that due to ice formation). Arctic and Antarctic insects, fish and amphibians create cryoprotectants (antifreeze, antifreeze compounds and antifreeze prot ...
s such as
polyol In organic chemistry, a polyol is an organic compound containing multiple hydroxyl groups (). The term "polyol" can have slightly different meanings depending on whether it is used in food science or polymer chemistry. Polyols containing two, thr ...
s and sugars, which reduce the whole body SCP. Although polyols such as
sorbitol Sorbitol (), less commonly known as glucitol (), is a sugar alcohol with a sweet taste which the human body metabolizes slowly. It can be obtained by reduction of glucose, which changes the converted aldehyde group (−CHO) to a primary alcohol g ...
,
mannitol Mannitol is a type of sugar alcohol used as a sweetener and medication. It is used as a low calorie sweetener as it is poorly absorbed by the intestines. As a medication, it is used to decrease pressure in the eyes, as in glaucoma, and to lower ...
, and
ethylene glycol Ethylene glycol (IUPAC name: ethane-1,2-diol) is an organic compound (a vicinal diol) with the formula . It is mainly used for two purposes, as a raw material in the manufacture of polyester fibers and for antifreeze formulations. It is an odo ...
can also be found,
glycerol Glycerol (), also called glycerine in British English and glycerin in American English, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...
is by far the most common cryoprotectant and can be equivalent to ~20% of the total body mass. Glycerol is distributed uniformly throughout the head, the thorax, and the abdomen of insects, and is in equal concentration in intracellular and extracellular compartments. The depressive effect of glycerol on the supercooling point is thought to be due to the high
viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...
of glycerol solutions at low temperatures. This would inhibit INA activityZachariassen KE (1985) Physiological Reviews: Physiology of Cold Tolerance in Insects. The American Physiological Society 65:799832 and SCPs would drop far below the environmental temperature. At colder temperatures (below 0 °C), glycogen production is inhibited, and the breakdown of glycogen into glycerol is enhanced, resulting in the glycerol levels in freeze-avoidant insects reaching levels five times higher than those in freeze tolerant insects which do not need to cope with extended periods of cold temperatures. Though not all freeze-avoidant insects produce polyols, all hibernating insects produce thermal hysteresis factors (THFs). For example, the
haemolymph Hemolymph, or haemolymph, is a fluid, analogous to the blood in vertebrates, that circulates in the interior of the arthropod (invertebrate) body, remaining in direct contact with the animal's tissues. It is composed of a fluid plasma in which ...
of the mealworm beetle ''
Tenebrio molitor Mealworms are the larval form of the yellow mealworm beetle, ''Tenebrio molitor'', a species of darkling beetle. Like all holometabolic insects, they go through four life stages: egg, larva, pupa, and adult. Larvae typically measure about or ...
'' contains a family of such proteins. A seasonal
photoperiodic A circadian rhythm (), or circadian cycle, is a natural, internal process that regulates the sleep–wake cycle and repeats roughly every 24 hours. It can refer to any process that originates within an organism (i.e., endogenous Endogenous subs ...
timing mechanism is responsible for increasing the
antifreeze protein Antifreeze proteins (AFPs) or ice structuring proteins refer to a class of polypeptides produced by certain animals, plants, fungi and bacteria that permit their survival in temperatures below the freezing point of water. AFPs bind to small i ...
levels with concentrations reaching their highest in the winter. In the pyrochroid beetle, ''Dendroides canadensis'', a short photoperiod of 8 hours light and 16 hours of darkness, results in the highest levels of THFs, which corresponds with the shortening of daylight hours associated with winter. These antifreeze proteins are thought to stabilize SCPs by binding directly to the surface structures of the ice crystals themselves, diminishing crystal size and growth. Therefore, instead of acting to change the biochemistry of the bodily fluids as seen with cryoprotectants, THFs act directly with the ice crystals by adsorbing to the developing crystals to inhibit their growth and reduce the chance of lethal freezing occurring.


Freeze tolerance

Freeze tolerance in insects refers to the ability of some species to survive ice formation within their tissues. Insects that have evolved freeze-tolerance strategies manage to avoid tissue damage by controlling where, when, and to what extent ice forms. In contrast to freeze avoiding insects that are able to exist in cold conditions by
supercooling Supercooling, also known as undercooling, is the process of lowering the temperature of a liquid or a gas below its melting point without it becoming a solid. It achieves this in the absence of a seed crystal or nucleus around which a crystal ...
, freeze tolerant insects limit supercooling and initiate the freezing of their body fluids at relatively high temperatures. Some insects accomplish this through inoculative freezing, while others produce cryoprotectants to control the rate of ice formation.Lee RE and Costanzo JP (1998) Biological ice nucleation and ice distribution in cold-hardy ectothermic animals. ''Annual Review of Physiology''. 60:55–72 Freezing at higher temperatures is advantageous because the rate of ice formation is slower, allowing the insect time to adjust to the internal changes that result from ice formation. Most freeze-tolerant species restrict ice formation to extracellular spaces, as intracellular ice formation is usually lethal. Some species, however, are able to tolerate intracellular freezing. This was first discovered in the
fat body 300px, Stained cells of an insect fat body Fat body is a highly dynamic insect tissue composed primarily of storage cells. It is distributed throughout the insect's internal body cavity; the haemocoel, in close proximity to the epidermis, dige ...
cells of the goldenrod gall fly ''Eurosta solidaginis''. The fat body is an insect tissue that is important for lipid, protein and carbohydrate metabolism (analogous to the mammalian liver). Although it is not certain why intracellular freezing is restricted to the fat body tissue in some insects, there is evidence that it may be due to the low water content within fat body cells. Although freeze-avoidance strategies predominate in the insects, freeze tolerance has evolved at least six times within this group (in the
Lepidoptera Lepidoptera ( ) is an order (biology), order of insects that includes butterfly, butterflies and moths (both are called lepidopterans). About 180,000 species of the Lepidoptera are described, in 126 Family (biology), families and 46 Taxonomic r ...
,
Blattodea Blattodea is an order of insects that contains cockroaches and termites. Formerly, termites were considered a separate order, Isoptera, but genetic and molecular evidence suggests they evolved from within the cockroach lineage, cladistically ...
,
Diptera Flies are insects of the order Diptera, the name being derived from the Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advanced ...
,
Orthoptera Orthoptera () is an order of insects that comprises the grasshoppers, locusts, and crickets, including closely related insects, such as the bush crickets or katydids and wētā. The order is subdivided into two suborders: Caelifera – grassho ...
,
Coleoptera Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...
, and
Hymenoptera Hymenoptera is a large order (biology), order of insects, comprising the sawfly, sawflies, wasps, bees, and ants. Over 150,000 living species of Hymenoptera have been described, in addition to over 2,000 extinct ones. Many of the species are Par ...
).Sinclair BJ, Addo-Bediako A, and Chown SL (2003) Climatic variability and the evolution of insect freeze tolerance. ''Biological Reviews'' 78:181195 Examples of freeze tolerant insects include: the woolly bear, ''
Pyrrharctia isabella ''Pyrrharctia isabella'', the isabella tiger moth, whose larval form is called the banded woolly bear, woolly bear, or woolly worm, occurs in the United States and southern Canada. It was first formally named by James Edward Smith in 1797. D ...
''; the flightless midge, ''
Belgica antarctica ''Belgica antarctica'', the Antarctic midge, is a species of flightless midge, endemic to the continent of Antarctica. At long, it is the largest purely terrestrial animal native to the continent. It also has the smallest known insect genome as ...
''; the alpine tree weta, '' Hemideina maori''; and the alpine cockroach, ''
Celatoblatta quinquemaculata ''Celatoblatta'' is a genus of cockroaches in the family Blattidae with species from Australia, New Zealand and New Caledonia ) , anthem = "" , image_map = New Caledonia on the globe (small islands magnified) (Polynesia centered).svg , map ...
''. Freeze tolerance is more prevalent in insects from the Southern Hemisphere (reported in 85% of species studied) than it is in insects from the Northern Hemisphere (reported in 29% of species studied). It has been suggested that this may be due to the Southern Hemisphere's greater climate variability, where insects must be able to survive sudden cold snaps yet take advantage of unseasonably warm weather as well. This is in contrast to the Northern Hemisphere, where predictable weather makes it more advantageous to overwinter after extensive seasonal cold hardening.


Ice nucleators

Freeze-tolerant insects are known to produce ice nucleating proteins. The regulated production of ice nucleating proteins allows insects to control the formation of ice crystals within their bodies. The lower an insect's body temperature, the more likely it is that ice will begin to form spontaneously. Even freeze-tolerant animals cannot tolerate a sudden, total freeze; for most freeze-tolerant insects it is important that they avoid supercooling and initiate ice formation at relatively warm temperatures. This allows the insect to moderate the rate of ice growth, adjust more slowly to the mechanical and osmotic pressures imposed by ice formation.Storey KB and Storey JM (1988) Freeze tolerance in animals. ''Physiological Reviews'' 68:27–84 Nucleating proteins may be produced by the insect, or by microorganisms that have become associated with the insects' tissues. These microorganisms possess proteins within their cell walls that function as nuclei for ice growth. The temperature that a particular ice nucleator initiates freezing varies from molecule to molecule. Although an organism may possess a number of different ice nucleating proteins, only those that initiate freezing at the highest temperature will catalyze an ice nucleation event. Once freezing is initiated, ice will spread throughout the insect's body.


Cryoprotectants

The formation of ice in the extracellular fluid causes an overall movement of water out of cells, a phenomenon known as
osmosis Osmosis (, ) is the spontaneous net movement or diffusion of solvent molecules through a selectively-permeable membrane from a region of high water potential (region of lower solute concentration) to a region of low water potential (region of ...
. As too much dehydration can be dangerous to cells, many insects possess high concentrations of solutes such as glycerol. Glycerol is a relatively polar molecule and therefore attracts water molecules, shifting the osmotic balance and holding some water inside the cells. As a result, cryoprotectants like glycerol decrease the amount of ice that forms outside of cells and reduce cellular dehydration. Insect cryoprotectants are also important for species that avoid freezing; see description above


Locations of hibernating insects

Insects are well hidden in winter, but there are several locations in which they can reliably be found.
Ladybug Coccinellidae () is a widespread family of small beetles ranging in size from . They are commonly known as ladybugs in North America and ladybirds in Great Britain. Some entomologists prefer the names ladybird beetles or lady beetles as they ...
s practice communal hibernation by stacking one on top of one another on stumps and under rocks to share heat and buffer themselves against winter temperatures. The female
grasshopper Grasshoppers are a group of insects belonging to the suborder Caelifera. They are among what is possibly the most ancient living group of chewing herbivorous insects, dating back to the early Triassic around 250 million years ago. Grasshopp ...
(family Tettigoniidae [long-horned]), in an attempt to keep her eggs safe through the winter, tunnels into the soil and deposits her eggs as deep as possible in the ground. Many other insects, including various
butterflies Butterflies are insects in the macrolepidopteran clade Rhopalocera from the Order (biology), order Lepidoptera, which also includes moths. Adult butterflies have large, often brightly coloured wings, and conspicuous, fluttering flight. The ...
and
moth Moths are a paraphyletic group of insects that includes all members of the order Lepidoptera that are not butterflies, with moths making up the vast majority of the order. There are thought to be approximately 160,000 species of moth, many of w ...
s also overwinter in soil in the egg stage. Some adult
beetle Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...
s hibernate underground during winter; many flies overwinter in the soil as pupae. The western malaria mosquito overwinters as adults, traveling between multiple human structures throughout the winter. Other methods of hibernation include the inhabitance of bark, where insects nest more toward the southern side of the tree for heat provided by the sun. Cocoons,
gall Galls (from the Latin , 'oak-apple') or ''cecidia'' (from the Greek , anything gushing out) are a kind of swelling growth on the external tissues of plants, fungi, or animals. Plant galls are abnormal outgrowths of plant tissues, similar to be ...
s, and
parasitism Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted structurally to this way of lif ...
are also common methods of hibernation.


Aquatic insects

Insects that live under the water have different strategies for dealing with freezing than terrestrial insects do. Many insect species survive winter not as adults on land, but as larvae underneath the surface of the water. Under the water many
benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...
invertebrates will experience some subfreezing temperatures, especially in small streams. Aquatic insects have developed freeze tolerance much like their
terrestrial Terrestrial refers to things related to land or the planet Earth. Terrestrial may also refer to: * Terrestrial animal, an animal that lives on land opposed to living in water, or sometimes an animal that lives on or near the ground, as opposed to ...
counterparts. However, freeze avoidance is not an option for aquatic insects as the presence of ice in their surroundings may cause ice nucleation in their tissues. Aquatic insects have supercooling points typically around −3º to −7°C. In addition to using freeze tolerance, many aquatic insects migrate deeper into the water body where the temperatures are higher than at the surface. Insects such as
stoneflies Plecoptera is an order of insects, commonly known as stoneflies. Some 3,500 species are described worldwide, with new species still being discovered. Stoneflies are found worldwide, except Antarctica. Stoneflies are believed to be one of the mo ...
,
mayflies Mayflies (also known as shadflies or fishflies in Canada and the upper Midwestern United States, as Canadian soldiers in the American Great Lakes region, and as up-winged flies in the United Kingdom) are aquatic insects belonging to the orde ...
,
caddisflies The caddisflies, or order Trichoptera, are a group of insects with aquatic larvae and terrestrial adults. There are approximately 14,500 described species, most of which can be divided into the suborders Integripalpia and Annulipalpia on the b ...
, and
dragonflies A dragonfly is a flying insect belonging to the infraorder Anisoptera below the order Odonata. About 3,000 extant species of true dragonfly are known. Most are tropical, with fewer species in temperate regions. Loss of wetland habitat threa ...
are common overwintering aquatic insects. The dance fly
larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...
e have the lowest reported supercooling point for an aquatic insect at −22°C.


See also

*
Cryobiology Cryobiology is the branch of biology that studies the effects of low temperatures on living things within Earth's cryosphere or in science. The word cryobiology is derived from the Greek words κρῧος ryos "cold", βίος ios "life", and λό ...
*
Overwinter Overwintering is the process by which some organisms pass through or wait out the winter season, or pass through that period of the year when "winter" conditions (cold or sub-zero temperatures, ice, snow, limited food supplies) make normal activi ...


References


External links

* * * * {{DEFAULTSORT:Insect Winter Ecology Winter ecology
Winter Winter is the coldest season of the year in polar and temperate climates. It occurs after autumn and before spring. The tilt of Earth's axis causes seasons; winter occurs when a hemisphere is oriented away from the Sun. Different cultures ...
Winter phenomena