# Long-tailed giant ichneumon wasp (Megarhyssa macrurus) > A very long-ovipositor parasitic wasp that searches dead wood for horntail larvae; harmless to people and beneficial in controlling wood-boring insects. Source: https://insectscanner.com/species/long-tailed-giant-ichneumon-wasp/ (updated 2026-10-10) ## Is it dangerous? **Non-toxic.** Megarhyssa macrurus does not have a stinger for human use; the long ovipositor is used to insert eggs into wood and is not a venom-injecting stinger. They are non-aggressive and rarely, if ever, pierce human skin. No medical treatment is normally needed. If an unusual puncture occurs, clean the area, apply antiseptic, and seek medical care if there is persistent pain, swelling or signs of infection. **Pets:** Not dangerous to pets. Very unlikely to sting or harm cats or dogs; they are not interested in attacking animals. ## Quick facts - Scientific name: Megarhyssa macrurus - Also called: Giant Ichneumon, Long-tailed wasp - Order: Hymenoptera (Bees, wasps and ants) - Family: Ichneumonidae (Ichneumon wasps) - Size: Female body about 3.5-5 cm; ovipositor up to about 10 cm or more beyond the body - Colours: Yellow, Orange-brown, Dark brown, Black - Habitat: Deciduous and mixed forests, woodland edges, and areas with dead standing trees or fallen logs where horntail hosts live - Range: Eastern and central North America (United States and southern Canada), tied to ranges of wood-boring horntail hosts - Active: Late spring through summer (when adults fly and mate); daytime active, often seen on warm, sunny days - Lifespan: Adults live days to a few weeks; full development from egg to adult spans months and depends on host development - Effect on plants: Pest predator - Pest: no ## Overview Megarhyssa macrurus is a large, slender ichneumonid wasp native to North American forests. Females have an extremely long ovipositor used to drill into dead or dying wood to lay eggs on the larvae of wood-boring horntail wasps. Adults are non-aggressive, feed on nectar, and are most often seen near fallen or standing dead trees where host larvae occur. They are solitary parasitoids: each Megarhyssa larva develops by consuming a single host. ## How to identify it Adults are very long and slender with long legs and a narrow 'waist'. Males lack the long ovipositor and are noticeably shorter. Females carry a thread-like ovipositor that can be about twice the length of the body. Body pattern is a mix of yellow to orange and dark brown or black banding; wings are clear to slightly smoky with visible venation. The overall impression is delicate and stick-like rather than robust. - Very long, thread-like ovipositor on females that extends well beyond the rear of the body - Slender, elongated body with contrasting yellow/orange and dark brown or black banding - Long legs and clear to slightly smoky wings with visible venation - Large overall length compared with common wasps; males are smaller and lack the long ovipositor ## Lookalikes - **Black Giant Ichneumon** (Megarhyssa atrata): M. atrata is darker overall (more black) and usually has less yellow/orange; ovipositor present in females as well but body patterning differs. - **Megarhyssa greenei** (Megarhyssa greenei): Similar long-ovipositor species; differences are subtle and require close comparison of body markings and geographic range. ## Life cycle - **Egg:** Female drills an ovipositor through bark into wood and lays eggs on or near a horntail larva, usually within tunnels in dead or dying wood. - **Larva (parasitoid):** Megarhyssa larva feeds on the horntail host, feeding externally on it while protected inside the wood, where it overwinters. - **Pupa:** After consuming the host, the wasp larva pupates inside a chamber within the wood and develops into an adult. - **Adult:** Adult wasps emerge from the wood, mate, feed on nectar, and females search for hosts to repeat the cycle. ## Diet and predators - Young eat: Ectoparasitoid of horntail (Siricidae) larvae, especially the pigeon tremex (Tremex columba), that bore in dead or dying hardwoods; the larva feeds externally on its host - Adults eat: Nectar from flowers, sometimes honeydew - Predators of the young: Probably exposed to wood-associated predators and parasitoids, but specific predators are poorly documented - Predators of adults: Birds, larger predatory insects and spiders may take adults ## Effect on plants and gardens Indirectly beneficial: Megarhyssa larvae parasitize wood-boring horntail larvae that can damage dead or weakened trees. Adults feed on nectar and can visit flowers but are not important pollinators compared with bees. ## Where and when to find it Look on or near dead standing trees, fallen logs, and old stumps. Adults visit nearby flowers for nectar; females inspect bark and drill with the ovipositor into wood. - Best time: Late spring through summer, during warm, sunny daylight hours. - Tips: Photograph from a distance to avoid disturbing the insect; a macro lens helps capture the long ovipositor and banded body. Look for emergence holes in dead wood as signs of past activity. ## Fun facts - The female's ovipositor is not a stinger; it is an egg-laying organ that can be about twice as long as her body. - Females can detect horntail larvae living deep in wood and drill to reach them using the ovipositor. - Despite their intimidating look, they are harmless to humans and are beneficial biological control agents. ## Frequently asked questions ### Do long-tailed giant ichneumon wasps sting people? No. The long structure on females is an ovipositor used to lay eggs into wood, not a venomous stinger. They are not aggressive toward people. ### Are long-tailed giant ichneumon wasps dangerous? No. They pose virtually no danger to humans or pets. They do not seek out or attack people. ### Why is one in my yard or on my house? Females are searching for wood-boring horntail larvae inside dead or dying wood. If you have fallen logs, dead limbs, or old fence posts nearby, that attracts them. ### How do I get rid of them? They are beneficial, so the best approach is to leave them alone. If they are unwanted near housing, remove or dispose of infested dead wood and keep firewood stacked away from the house. Avoid spraying broad insecticides because that kills beneficial insects. ### Where do they live and when will I see them? They live where horntail hosts occur: forests and wooded areas with dead or decaying trees. Adults are active in late spring and summer on warm days. --- More about this species: [iNaturalist](https://www.inaturalist.org/taxa/47963), [Wikipedia](https://en.wikipedia.org/wiki/Megarhyssa_macrurus). Identify insects and spiders from a photo with the Insect Scanner iPhone app: https://apps.apple.com/app/id1543946563?pt=126685406&ct=web-markdown&mt=8 Identification from photos is never certain: don't handle insects you can't identify, and get medical advice for bites, stings or allergic reactions.