Adults are usually 7–12 mm long.
Fine-art photographic collection
Tromatobia lineatoria
A wasp that drills through a spider’s silk nursery and turns the protected eggs inside into food for its own offspring.
About this species
Tromatobia lineatoria(Villers, 1789)
Information reviewed15 July 2026
Tromatobia lineatoria is a European ichneumon wasp specialised on spider egg sacs. The female locates the silk package, pierces it with her ovipositor and lays eggs among the spider’s eggs.
Taxonomy
Animalia · Arthropoda · Insecta · Hymenoptera · Ichneumonidae · Pimplinae · Tromatobia
Accepted taxon. · checked 2026-07-15
Europe and temperate western AsiaBroad range and selected reference localities — not a complete occurrence map.
Europe and temperate western Asia
Woodland, gardens, hedgerows and scrub where orb-weavers and crab spiders place egg sacs.
Adults fly in warmer months; females search vegetation and bark for spider egg sacs.
Adults take nectar; larvae consume spider eggs within the sac.
Solitary parasitoid or predator of spider egg masses.
What makes this species remarkable?
The female detects a spider egg sac through its silk covering and pushes a slender ovipositor through the wall without opening the nursery.
Her larvae hatch inside and eat spider eggs one after another; biologically they behave more like predators in a sealed food chamber than conventional one-host parasitoids.
The wasp then pupates inside the same protective silk structure built by the spider, converting the host’s nursery into both pantry and shelter.
Sources and scientific references
- GBIF — taxon record/search for Tromatobia lineatoria
- Catalogue of Life — taxon search for Tromatobia lineatoria
- Open-access review of parasitoids and predators of spider egg sacs
- Contributions to Zoology — evolutionary biology of polysphinctine and tromatobiine spider parasitoids
- Species account and host records for Tromatobia lineatoria