- Also called:
- ichneumonid wasp or Darwin wasp
- Related Topics:
- wasp
- parasitoid
- Ichneumonoidea
- Lissopimpla
ichneumon wasp
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What is an ichneumon wasp?
Ichneumon wasps are parasitoids whose larvae feed on other arthropods, especially caterpillars, beetles, and other wasps. Adults average about 0.5 inch long, though some North American species reach over 2 inches, not counting the ovipositor (egg-laying organ), which can add another 2 to 4 inches.
Adult ichneumon wasps eat nectar and pollen, and females lay eggs in or on the host larva or pupa. Some species bore into wood to reach hosts, and some can sting. Most develop as a single larva in one host, but some have multiple larvae per host. They play an important role in regulating insect populations, especially pests, and are sometimes used for biological control.
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What do ichneumon wasps look like?
Ichneumon wasps exhibit considerable diversity in size, color, and shape, with adults typically averaging around 1.2 cm in length, though some can be larger. The Megarhyssa, the biggest ichneumons in North America, can reach lengths of more than 5 cm, not including the ovipositor, which can be 5 to 10 cm long in females.
Ichneumon wasps have a head, thorax, and abdomen, as well as six legs, similar to other insects. They have three ocelli (simple eyes) on top of their heads and a pair of large compound eyes on the sides. Most have a slender, curved abdomen and a narrow waist, similar to other wasps. However, they often differ from stinging wasps, as they have longer antennae with more segments. Many species have a dark spot on the fore wing.
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Where can ichneumon wasps be found?
Ichneumon wasps are a large, widely distributed solitary wasp family of considerable ecological and economic importance. As one of the most diverse animal groups, they can be found worldwide in both temperate and tropical regions. The western giant ichneumonid wasp, for example, has been introduced to South Africa, Australia, and New Zealand as a biological control agent.
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How do ichneumon wasps reproduce?
Ichneumon wasps reproduce as parasitoids, where their larvae grow on other arthropods. Adult wasps gather to mate, and females deposit eggs in the larvae or pupae of a host, though sometimes in the eggs or adults. Some species can drill into wood to reach hosts. After hatching, the larva consumes the host's fluids until it grows, then it spins a cocoon or pupates inside the host's body. Ichneumon wasps that target hosts in open areas typically grow as internal endoparasites, while those that attack hosts in concealed places feed on the host externally as ectoparasites. Usually, only one larva matures in a host, but sometimes many can.
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What do ichneumon wasps eat or feed on?
Ichneumon wasp larvae are parasitoids that feed on arthropods, such as Lepidoptera (moths and butterflies) and Coleoptera (beetles). The ichneumon wasp larvae feed on the host's body fluids and fats until fully grown. Adult ichneumon wasps eat nectar and pollen and may also feed on fluids from punctures made by the ovipositor.
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How do ichneumon wasps help control pest populations in nature?
Ichneumon wasps play a vital role in regulating insect populations because their larvae kill their hosts. They parasitize numerous insect pests in natural and agricultural settings, helping to control their numbers. Certain ichneumon wasp species have been introduced to specific areas as biological control agents. For example, the western giant ichneumonid wasp was introduced to South Africa, Australia, and New Zealand to reduce the populations of the invasive wood wasp. Similarly, the yellow ichneumon wasp is an economically important parasitoid of stem-boring caterpillars that feed on cereal plants and other crops.
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ichneumon wasp, (family Ichneumonidae), any of a large and widely distributed solitary wasp family of considerable ecological and economic importance. One of the most diverse animal groups in the world and the largest group of parasitic wasps, there are around 25,000 ichneumon wasp species known to science and as many as 75,000 more that are yet to be discovered and named.
The name sometimes refers to any member of the superfamily Ichneumonoidea, which includes the families Stephanidae, Braconidae, and Ichneumonidae. The Stephanidae, a largely tropical group, consists of several hundred species, and the Braconidae is a large, widely distributed group found in both temperate and tropical regions.
- Kingdom: Animalia
- Phylum: Arthropoda
- Class: Insecta
- Order: Hymenoptera
- Suborder: Apocrita
See also list of ants, bees, and wasps.
Physical description
Given the sheer number of species, ichneumon wasps vary considerably in shape, color, and size. Adults average about 1.2 cm (about 0.5 inch) long, though many are larger. The largest ichneumons of North America, those of the genus Megarhyssa, are more than 5 cm (2 inches) in length, not including the extremely long ovipositor (egg-laying organ) of the females, which may be 5 to 10 cm (2 to 4 inches) in length. Ichneumon wasps are similar in appearance, though typically larger in size, than the related braconid wasps, another group of parasitic wasps. Many species exhibit sexual dimorphism in which the coloration of the males and females differs.
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As insects, ichneumon wasps have a body formed of a head, thorax, and abdomen, and six legs. They have a pair of large compound eyes on the side of the head and three ocelli (simple eyes) on the top of the head. Most species resemble other wasps in having a long, slender, curved abdomen with a fairly narrow waist. They usually differ from the stinging wasps in having longer antennae with more segments, or sections. Often confused for an intimidating stinger, the ovipositor is generally longer than the body; only a few species use the ovipositor for defense. Many species have a dark spot on the fore wing.
Natural history and parasitism
Ichneumon wasps are parasitoids, meaning their larvae feed and develop on or within the bodies of other arthropods. They parasitize many insect groups, especially Lepidoptera (moths and butterflies), Coleoptera (beetles), and other Hymenoptera (ants, bees, and wasps). Some utilize spiders as hosts.
Adult wasps typically feed on nectar and pollen, and as solitary wasps, only come together to mate. The females lay their eggs in or on the larvae or pupae (rarely eggs or adults) of the host. To attack wood-boring hosts deep inside woody plant tissues, some ichneumon wasp species actually use their ovipositors as a drill capable of penetrating solid wood. Once the ichneumon wasp egg hatches, the larva feeds on the fats and body fluids of the doomed host until fully grown, then usually spins a silken cocoon or pupates within the host’s body. The species that parasitize hosts in open habitats usually develop as internal endoparasites, whereas those that attack hosts in concealed places, such as wood burrows, usually feed on the host externally as ectoparasites. In most cases a single larva develops in one host. However, in some cases, many larvae develop in a single host.
Members of the subfamily Ophioninae, including Ophion, Enicospilus, and Thyreodon, primarily parasitize moths and are thus active at night. They form one of the few groups of ichneumon wasps that can sting vertebrate animals. Certain members of the genus Netelia (subfamily Tryphoninae) also use their short ovipositors defensively.
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“I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidæ with the express intention of their feeding within the living bodies of Caterpillars.”
A few species are hyperparasitic, meaning they feed on the primary parasitoid already developing within the original host. Such species attack a wide range of insects parasitized by other hymenopterans, including heteroperans (true bugs), lepidopterans, and symphytans (sawflies, horntails, and wood wasps).
Importance
Ichneumon wasp larvae kill their hosts and thus fulfill an important role in the regulation of insect populations. The group parasitizes many insect pests, serving to keep their abundance in check in both natural and agricultural settings, and only small number of species parasitize other beneficial insects. Specific ichneumon wasps have been actively encouraged or introduced in some places to serve as biological control. The western giant ichneumonid wasp (Megarhyssa nortoni), for example, has been introduced to South Africa, Australia, and New Zealand as a biological control agent to reduce the populations of the invasive wood wasp Sirex noctilio. Similarly, the yellow ichneumon wasp (Xanthopimpla punctata) is an economically important parasitoid of stem boring caterpillars that feed on cereal plants and other crops.
Beyond their parasitism, ichneumon wasps are also at least incidental pollinators for many plant species. The group is understudied, but there is evidence that some species have a degree of floral specialization and exhibit specific foraging behaviors, suggesting that their importance as pollinators may be under appreciated.