Sibine stimulea
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The saddleback caterpillar (''Acharia stimulea'', formerly ''Sibine stimulea'') is the larva of a species of moth native to eastern North America. It is also found in Mexico. The species belongs to the family of slug caterpillars, Limacodidae. The larva (caterpillar) is primarily green with brown at both ends and a prominent white-ringed brown dot in the center which resembles a saddle. It has a pair of fleshy horns at both ends. These and most of the rest of the body bear urticating hairs that secrete an irritating venom. Contact with the hairs causes a painful, swollen rash and sometimes nausea in humans. In some cases, more severe reactions to the venom can occur, including a systemic condition called erucism or acute urticaria, for which severe symptoms may include
migraine Migraine (, ) is a common neurological disorder characterized by recurrent headaches. Typically, the associated headache affects one side of the head, is pulsating in nature, may be moderate to severe in intensity, and could last from a few hou ...
s, gastrointestinal symptoms, asthma complications,
anaphylactic shock Anaphylaxis is a serious, potentially fatal allergic reaction and medical emergency that is rapid in onset and requires immediate medical attention regardless of use of emergency medication on site. It typically causes more than one of the follow ...
, rupturing of erythrocytes, and hemorrhaging. The hairs should be removed from the skin immediately to prevent more venom spread. The cocoon may also have irritating hairs, and hairs from the larva can fall on surrounding objects.Bibbs, C. S. and J. H. Frank
''Acharia stimulea'' (Clemens) (Insecta: Lepidoptera: Limacodidae).
EENY-522. University of Florida IFAS. 2012.
The larvae feed on a large variety of plants. In Florida and Alabama in the United States, it feeds on ornamental palms such as the Manila palm (''Adonidia merrillii'').


Description

''Acharia stimulea'' (formally known as ''Sibine stimulea'') is a moth of the family Limacodidae that is most widely known and recognizable for its larvae phase. During the mid and late instar (a phase between two periods of molting in the development), ''Acharia stimulea'' exhibits its characteristic lime-green coloring along the top of the body that contains its most identifiable feature, a dark marking at the center that is inclosed in a white and black that resembles a saddle. The green of the body contrasts against its dark anterior (head ) and posterior (rear) which, along with the skirt of the body, contain tubercles with hollow spines that, when broken, release an irritating toxin into predators. Like others in the family Limacodidae, they rely on their slug-like anatomy to move. Similar to a slug, ''Acharia stimulea'' uses suckers and mucus to help them roll and adhere to surfaces.Hyche, L. L
Stinging Caterpillars: A Guide to Recognition of Species Found on Alabama Trees.
Entomology. Auburn University. 1998.
After pupation the adult ''Acharia stimulea'' loses all of its vibrant coloring and develops velvety dark brown anterior wings and cream posterior wings. File:- 4700 – Acharia stimulea – Saddleback Caterpillar (44277843172).jpg, alt=formally known as Sibine stimulea, commonly known as the Saddleback caterpillar)., Saddleback caterpillar (larvae form of ''Acharia stimulea'') File:Acharia stimulea.jpg, alt=(formally known as Sibine stimulea, commonly known as the Saddleback caterpillar)., Adult form of ''Acharia stimulea''


Distribution and habitat

''Acharia stimulea'' are native to
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 ...
and are most known for living in warmer climates like Yucatan, Mexico but they can also survive the slightly cooler temperatures of the eastern United States. Adult moths fly during warm months which can be year round in the south or between July and August in the U.S. ''Acharia stimulea'' are
polyphagous Feeding is the process by which organisms, typically animals, obtain food. Terminology often uses either the suffixes -vore, -vory, or -vorous from Latin ''vorare'', meaning "to devour", or -phage, -phagy, or -phagous from Greek φαγε ...
and do not rely on a single plant species for survival though they tend to favor palms. Below is a list of known host plants that the ''Acharia stimulea'' female moths are known to lay their egg on and where they live during their larvae phase:


Life cycle

Stages of
metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...
:


Eggs

The mother ''Acharia stimulea'' will lay her
egg An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the a ...
s 3 days after mating on the underside of a
host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County People *Jim Host (born 1937), American businessman * Michel Host ...
plant's leaf, laying clusters of 30-50 eggs at a single time with an average of 300 in total. Each egg is around 1.5-2.0mm long and 1mm wide. Similar to other eggs of the family Limacodidae, ''Acharia stimulea'' eggs are flat and are a translucent lime green color when first laid by the mother. As they get closer to hatching the eggs become a translucent yellow and shriveled. Eclosion (the emergence of larvae from eggs) can take up to 10 days and the newly emerged larvae will feed on the underside of a leaf's
epidermis The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water rele ...
until their first molt.


Larvae

Throughout its life as a larva the saddleback caterpillar will go through a series of growths and molts. During the period between each molt the larva is regarded as an instar to indicate its progression into adulthood. The first instar: Caterpillar larvae vary in size and are capable of being between 1.5-2.0mm in length. At this stage a hatchling lacks its characteristic coloring and instead tends to be a translucent lime green with green or black tentacles and green protuberances along the skirt which lack the long spiny thorns that are seen in older larvae. While it also lacks the recognizable saddled back, there may be markings on the body that indicate where the saddle will be as the top of some hatchlings tend to have a white or a slightly darker green marking on its top center. The middle instar: Occurs during the second to fourth molt and is the period in time where the larva begins to gain its characteristic markings. Here, the top of the body gains a more opaque green that differentiates the top of the body from the bottom and contains a black dot, commonly called a "saddle", at the center that is held within a white oval shape that is surrounded by a black outlining. At this stage the tentacles also gain their coloring. The tentacles usually become darker with age, starting as green when hatched and then becoming orange around the middle instar. Some ''Acharia stimulea'' will also develop a facial marking with two cream or light-green markings that mimic large eyes at the posterior end of the body. The protuberances along the bottom sides of the larvae also become orange at this stage. Thorns on the tentacles and the protuberances along the side of the body also begin to elongate and obtain their stinging nature, with those on the tentacles being longer in length. At this stage larvae will also begin to eat plant tissue and grow to be about 5-8mm in size. Late instar: ''Acharia stimulea'' is most known for its late instar stage where it is easily identifiable through its unique marking that has become more vibrant.  As the anterior and posterior range from being a vibrant orange, brown, or dark purple the top of the body has turned into a more vibrant green. The caterpillars' green body with its characteristic “saddle” has also become well defined with its color having developed into a dark-orange or brown color with each of its molts. At this stage, the thorns along the tentacles and tuburances have also become well developed and elongated. About four to five months after hatching the caterpillar will have reached its final instar and will begin to feed on both sides of the leaf and leaf tissue to ready itself for pupating. Before spinning its cocoon, an individual larva can reach measurements close to 20mm long and 7mm wide.


Pupa

While pupating the cocoon appears to be a hardened light brown spherical shape with black veining that is encompassed in silk webbing. This webbing is made up in part by caterpillars’ stinging thorns which helps attach and protect the caterpillar through its metamorphosis.


Adult

''Acharia stimulea'' emerge in June and July with females tending to be larger in size than their male counterparts. ''Acharia'' moths are not dimorphic in color as both males and females have dark brown anterior wings, cream, posterior wings, and a dark brown body. Like in other moths in the family Limacodidae, the wings and body appear to have a velvety fur-like texture. One of the main characteristics of ''Acharia stimulea'' at this stage is the presence of white dots that occur with about one or three at the apex and one at the inner middle of the anterior wings. Their wings can also reach a wingspan of  30mm. At this stage ''Acharia stimulea'' lack envenomation and live 10 days on average.


Gallery of the life cycle

File:Acharia stimulea 1274070.jpg, alt=Larvae form of Acharia stimulea during a mid instar, Mid instar File:Saddleback caterpillar - Acharia stimulea, Prince William Forest Park, Triangle, Virginia.jpg, Late instar File:Saddleback Caterpillar Remains - Flickr - treegrow.jpg, alt=Larvae remains of Acharia stimulea, Saddleback caterpillar remains File:Acharia stimulea 5020019.jpg, alt=Acharia stimulea cacoon, Pupa File:- 4700 – Acharia stimulea – Saddleback Caterpillar Moth (19866363376).jpg, alt=Final stage of acharia stimulea, Adult ''Acharia stimulea''


Reproduction

Adult ''Acharia stimulea'' will mate as soon as two days after emerging from their cocoon and will
copulate Sexual intercourse (or coitus or copulation) is a sexual activity typically involving the insertion and thrusting of the penis into the vagina for sexual pleasure or reproduction.Sexual intercourse most commonly means penile–vaginal penetrat ...
for up to 24 hours. In the wild mating rituals occur during nights with warm temperatures, which can vary between February and July in the United States. After mating the female will choose a host plant and lay her eggs on the underside of the leaf where she will frequently visit until they have successfully hatched.


Defense against predators

''Acharia stimulea'' has two distinct defense mechanisms, aposematism and mimicry.


Aposematism

''Acharia stimulea'' exhibits aposematic coloring which is a distinct vibrant coloring that represents their toxicity. Along the anterior, posterior and skirt of the caterpillar are tubercles that contain threatening hollow spines. While these spines are threatening alone, they actually go a step further in acting as a defense mechanism as they are connected to a gland that secretes venom that, when broken, is released into predators or unsuspecting gardeners. These spines are usually orange along the skirt of the caterpillar and orange or black along the tentacles present at both ends of the body. The larvae will use this defensively by curling outwards so that their spines are unavoidable to a predator. The spines are also used in the silk cocoon to further protect it during metamorphosis.


Mimicry

Throughout the larvae stage ''Acharia stimulea'' also exhibits a false face with two green or white dots that contrast against the dark coloring of the body that act as large eyes. While this marking resembles a face, it is actually located at the posterior of the Saddleback caterpillar. This is an example of defensive mimicry which can be seen in other moth species such as '' Deilephila elpenor'' (elephant hawk-moth) which exhibits snake like features in order to deter predators. It is not uncommon for these facial features to be represented on the posterior as it is believed to be used to misdirect predators and is often called automimicry or
intraspecific Biological specificity is the tendency of a characteristic such as a behavior or a biochemical variation to occur in a particular species. Biochemist Linus Pauling stated that "Biological specificity is the set of characteristics of living organ ...
mimicry In evolutionary biology, mimicry is an evolved resemblance between an organism and another object, often an organism of another species. Mimicry may evolve between different species, or between individuals of the same species. Often, mimicry f ...
.


Dangers and treatments of stings

''Acharia stimulea'' is known for having one of the strongest stings and due to the saddleback caterpillar being commonly found in ornamental plants, gardeners are most at risk to accidental exposure. The spines along the caterpillar, when broken, will release an irritating toxin into its victims that is known to cause acute urticaria in humans. These spines are fragile and can become airborne and embedded into surfaces therefore immediate action is required for removal if infected to prevent prolonged harm. Spines can be removed by using adhesive tape over the infected area to pull out the spines, with a new piece of tape used for each treatment. Symptoms can be mild or severe and can last from a few hours to a few days depending on the sensitivity of those infected and can be relieved through prescribed medication on a case-by-case basis. Some of the symptoms include
headache Headache is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches. Headaches can occur as a result ...
s, conjunctivitis, difficulty breathing,
gastrointestinal symptom Gastrointestinal diseases (abbrev. GI diseases or GI illnesses) refer to diseases involving the gastrointestinal tract, namely the oesophagus, stomach, small intestine, large intestine and rectum, and the accessory organs of digestion, the liver, g ...
s, asthma complications,
anaphylactic shock Anaphylaxis is a serious, potentially fatal allergic reaction and medical emergency that is rapid in onset and requires immediate medical attention regardless of use of emergency medication on site. It typically causes more than one of the follow ...
and hemorrhaging. Ice packs,
corticosteroid Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones. Two main classes of corticosteroids, glucocorticoids and mineralocorticoids, are involv ...
s, topical and oral antihistamines have been reported to help relieve pain.


Parasitism

The saddleback caterpillar are known to become frequently infested by the braconid wasp. A female braconid wasp will inject eggs in a venom like manner into its chosen host caterpillar, which is known as
ovipositing The ovipositor is a tube-like organ used by some animals, especially insects, for the laying of eggs. In insects, an ovipositor consists of a maximum of three pairs of appendages. The details and morphology of the ovipositor vary, but typical ...
. The parasitic wasp eggs are able to survive by feeding on the inside of the saddleback caterpillar and emerge as larvae by creating holes in the body. File:Aleiodes indiscretus wasp parasitizing gypsy moth caterpillar.jpg, alt=Aleiodes indiscretus ovipositing in its host, Example of ovipositing seen in the ''
Aleiodes indiscretus ''Aleiodes indiscretus'' is a species of parasitoid wasp Parasitoid wasps are a large group of hymenopteran superfamilies, with all but the wood wasps (Orussoidea) being in the wasp-waisted Apocrita. As parasitoids, they lay their eggs on ...
'' wasp File:Acharia stimulea 0007050.jpg, Parasitic braconid wasp larvae emerging from the saddleback caterpillar File:Acharia stimulea 0007051.jpg, Saddleback caterpillar with parasitic braconid wasp larvae File:Saddleback Caterpillar Remains - Flickr - treegrow (1).jpg, Saddleback Caterpillar remains


References


External links

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Additional images of the saddleback caterpillar
{{Taxonbar, from=Q1948552 Limacodidae Moths of North America Moths described in 1860 Taxa named by James Brackenridge Clemens