Tuesday, 19 August 2008
Ichneumonids are parasitic wasps which lay their eggs directly into the larvae of butterflies, moths, flies and sawflies, although some are hyperparasites (laying their eggs into the larvae of primary parasites), and a few are paraparasites ( laying their eggs into the larvae of hyperparasites). The host is always eventually killed by the parasite, usually in the pupal phase. Most Ichneumonids lay a single egg in each host, although some lay multiple eggs, and there are over 1750 different species in UK and Ireland, ranging from 2-3mm up to the largest at 8cm long. Due to the fact that the various different families converge on a very small number of colour patterns, identification is very complex and always requires trapping, killing and microscopic investigation. There are very few people who have embarked upon the years of study required to investigate this group, so they are relatively poorly understood. If I had a spare life I would certainly give them a go, because I find them absolutely fascinating. Their form varies enormously, although they all have long antennae and a very narrow 'waist' between the thorax and the abdomen. The nature of the host can usually be determined by looking at various characteristics of the parasite: size, length of legs, length of ovipositor.
I photographed this beauty last night:
Based on the size (3 cm. from nose to tail) alone, this one requires a very large host, and it will almost certainly parasitise one of the larger moths, such as the Drinker or Northern Eggar. The larva of the Elephant Hawk Moth is parasitised by the similarly-sized black and white Ichneumon Amblyjoppa proteus. [http://homepage.eircom.net/~hedgerow14/may30.htm shows the emergence sequence]
The next is a Macrocentrus sp., and the structure of the body is very carefully arranged: she has massively long antennae, very long rear legs and a very long ovipositor. These lay their eggs into fly and moth larvae hidden deep inside the seedheads of Thistles and Knapweed. The long legs are required to give her body enough clearance to spin the ovipositor 180 degrees towards her antennae.
You can see an action shot here.
This next one is smaller, and has short legs and a medium-length ovipositor. I suppose this will be parasitic on a small larva which is exposed on the surface, rather than hidden in a seedhead.
The configuration of this one bothered me for a while. It has extraordinarily long antennae, long legs and no visible ovipositor. So what could possibly be the reason for such a shape?
(hint, wasp males usually have long antennae, and male ichneumonids are rare).
Just to complete the story from yesterday, here is the larva of the Sawfly Nematus pavidus, with its body curled in the usual defensive posture.