Wednesday, 2 July 2014

More on Horseflies

Following on from Kim and Neil's record of a female Tabanus autumnalis at Summer Leys, Dave Jackson sent me a picture of another there, but this time a male. In many species of flies, but not all, the males can be distinguished from the females by having holoptic eyes - that is the eyes meet along the top and front of the head. Females are always dichoptic - having a separation between the eyes. Here is Dave's photo:

 Tabanus autumnalis Large Marsh Horsefly (c) Dave Jackson

I mentioned in the previous blog some of the smaller, more common species of horsefly (family Tabanidae) so I have added a couple of examples below. 

Chrysops relictus Twin-lobed Deerfly (c) John Showers

The above horsefly is one of the usual culprits when a nice walk in the country is spoilt by biting flies. They can be very persistant. It tends to like damp places, marshes and damp woodlands are favoured. I was once driven off doing a dragonfly count at Pitsford's Holcot Bay by deerflies attacking me. There are very similar other species that occur locally but in much fewer numbers so I always try to take one or two for closer examination.

Hybomitra bimaculata  Hairy-legged Horsefly (c) John Showers

Notice the eye patterns on the horseflies. They all have coloured eyes and some have distinctive bands or spots. These patterns fade on dead insects so you need to see them live and up-close and personal to appreciate their beauty! These patterns are useful clues to identification so worth noting.

Last Saturday we held our late June Hoverwatch survey at Old Sulehay Forest and Graham Warnes caught another of the medium sized horseflies there Hybomitra bimaculata Hairy-legged Horsefly. These are usually found in woodland rides. I have also found this species at Yardley Chase. Often the males can be seen hovering a few feet off the ground in bright sunshine. They are holding territories to await or attract a passing female.

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