Thanks to volunteer Robert King for his report and photos
Summer is a great time to seek some of our most colourful and incredible insects – the longhorn beetles. Approximately 1 in 3 of all the animal species on Earth is a beetle and the longhorns comprise some of the most attractive and distinctive. Britain has about 70 longhorn species, though a few are thought to be extinct, and a couple are accidental imports with timber products etc. At RSPB Pulborough Brooks we have recorded 7 species, though there are certainly more present that have yet to be recorded.
Despite the name, not all longhorns have long antennae, though those that do can be very striking. Such long sense organs are useful for seeking out the chemical signature that denotes a mate, or that gives away the location of decaying wood - a suitable site to lay eggs.
Longhorns spend most of their lives out of sight from us - as larvae, beetle ‘grubs’, feeding within dead and decaying wood. Some specialize in living in certain trees (e.g. conifers), or certain parts of the tree - such as roots or decaying sapwood - but all are doing a valuable job recycling and clearing up fallen branches and deadwood. Many longhorns are in decline due to the human race tidying of woodland habitats. Removing deadwood and felling dying trees destroys the rich habitat on which much of our wildlife relies. On the reserve we try to leave deadwood where possible and at home you can do your bit to help beetles by doing the same, or creating ‘habitat piles’ of logs left in a corner of your garden.
It takes a lot of munching to acquire all the nutrients required to grow, so beetle larvae can spend several years as a grub. When they are fully grown, longhorn larvae form a pupa and undergo a full metamorphosis. The body tissue breaks down and reforms to take the shape of an adult beetle.
For those rusty on beetle biology, adult longhorn beetles have the classic characteristics of beetles – six legs, hard exoskeleton and two pairs of wings. The outer pair of wings on beetles are called elytra and are thickened and hardened into a protective shell. On longhorns, these are often brightly coloured and striking, but beneath them are a pair of fully functioning wings, neatly folded out of sight.
Adult longhorns need to feed, disperse, find a mate and breed. All of these tasks give us opportunity to seek them out. In keeping with most insects, they need warmth, so your highest chances of finding one is to pick a warm sunny day. Many longhorn beetles will feed on flowers and this is a good way of finding them. Searching the flowers of bramble, umbellifers and hawthorn can be particularly productive, especially along woodland rides.
The photograph below was taken on the reserve on a sunny day in Black Wood. The beetle on the left is a female Black-striped Longhorn Beetle. Just coming into shot on the right is a second, perhaps a male, seeking out the female using his long antennae to pick up her ‘perfume’ – pheromones. You can just see his thin flight wings, whilst the hardened outer wings are held out of the way.
Having mated, the female longhorn will seek out a suitable location to lay her eggs. She may need to gnaw through bark in order to safely deposit her eggs, depending upon what conditions the larvae need to thrive. The photograph below shows a female Wasp Beetle laying eggs in a recently cut log. She deposits them individually using the ovipositor at the end of her abdomen.
Active during the day, longhorns run the risk of becoming a tasty snack for a hungry bird. The Wasp Beetle pretends to be something more dangerous than she is – her black and yellow colours mimic a wasp and she adds to the illusion by taking on the mannerisms of a wasp – she moves with a jerky stop - start action and flicks her antennae in wasp-like fashion.
Several of our longhorns have bright yellow and black colours, but no other has quite the mimicry skills of the Wasp Beetle. The Golden-haired Longhorn is sometimes called the Hornet Beetle – it’s a step up in size from the Wasp Beetle and when in flight is very impressive, though the flight style is very different to that of a Hornet! Whatever name you prefer, we’re proud to have a population of Golden-haired Longhorns - they are quite a rare beetle with a very restricted range in Britain. It can be separated from the more common and very similar looking Four-banded Longhorn (which is also be found at the reserve) by the presence of a band of golden coloured hairs that look like a collar behind the head.
Anna Allum
Another Longhorn which is always a treat to see is the huge Tanner Beetle. These all-black beetles can have a body length to 4.5cm, with their size amplified by the presence of long feathered antennae. Growing so large takes a long time – the larvae spend 3-4 years feeding deep in the roots of dead trees. The adults live under the cover of darkness – emerging at dusk and active through the night. It’s therefore seldom seen, most of our sightings are when one is attracted to a moth trap.
Not all longhorns feed on deadwood. The Golden-bloomed Grey Longhorn prefers the living stems of grassland plants, typically thistles and the like. Perhaps it is easier munching for the larvae to live in living plants rather than wood, as they get the whole larval stage done a year and are ready to emerge as adults in the following summer. We’ve not yet recorded this species from the reserve but it’s probably here, just waiting to be found and admired. If you find one and feel like picking one up then you might be in for a shock – this species can stridulate loudly if handled!
Hopefully this article will encourage you to look out for longhorns when you’re next at the reserve and to add to the records. You can log wildlife sightings using iRecord – the data will get fed back to the RSPB and help contribute to the understanding of these magical insects. Good luck!