Giant Black Tachinid

Tachina grossa

15-22mm

May to late August

This large bulky fly is often mistaken for a bumblebee at first glance – especially in flight. Fairly frequent where it occurs, but localised to heathland and downland where the host species are found. 

Male specimen, found on downland on the Isle of Wight

The larvae burrow into the caterpillars of large moths, often of the Oak Eggar, where they parasitize the host – feeding and developing within. Adults are most often seen in bright weather, feeding at umbellifers, creeping thistle and other wildflowers, or basking on bramble foliage.

Profile and Ventral views of a Male specimen

Both sexes are very similar – huge rounded black body covered in bristles, yellow or cream face with brown eyes and a yellow ‘collar’ of fur behind the head.

Wings have a clouded yellow region at their base.

Legs are black and bristly with large yellow pulvilli (foot pads).

Can exhibit aggressive or territorial behaviour towards smaller flies whilst feeding at flowers.

 Male specimen above, and much larger Female below

Tachina grossa hand drawn illustration,
pigment liner, markers, watercolour pencil & ink, A4
Prints available, signed and numbered limited edition.

An Illustrated diptych featuring Tachina grossa can be seen here, based on religious icons and sacred connotations:
https://www.flickr.com/photos/insectopolis/11187636574/