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Horntail Wasp

Sirex sp.


This is a Horntail Wasp or Wood Wasp of the Family Siricidae (Symphyta). She was found dying on the ground close to a new house in construction, where several of the pine trees had just been cut and were being shaped into beams. She undoubtedly had been busy placing her eggs in the wood. She is 2.5 cm in length, including the ovipositor. Interestingly, the ovipositor does not emerge from the tip as in most wasps, but farther in towards the base of the abdomen (see 5th picture). The ovipositor is also hinged, so that it can be moved perpendicular to the body for more effective penetration. Eggs are placed deep inside the wood along with a fungi that softens the wood for easier larval feeding. The females especially choose dead or weakened trees for their egg laying, which explains why she was at the construction site. The larval cycle can take from 2 to 5 years and often the wood is already part of a home's construction. The emerging adult has been known to bite through any type of covering on the wood, even metal panels. This one is completely blue-black in color, without any white or yellow markings on the head or legs. The wings are completely dark. She appears black in general, but at certain angles is metallic blue (see second picture). The head and thorax are sculptured and hairy. Horntails get their name from the odd, toothed horn-like structure at the end of the abdomen above the ovipositor (see pictures 1, 2, 4 & 5). They cannot sting. Family Siricidae, Siricinae.


Semi-rural residential area, San Cristobal de Las Casas, Chiapas, Mexico 2,200 meters.

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San Cristóbal, Chiapas, Mexico

Spotted on Jul 1, 2019
Submitted on Jul 3, 2019

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