DOWNLAND - OTHER INVERTEBRATES




 

 

Orthoptera (35 species of grasshoppers, crickets, earwigs and cockroaches in Britain) have an excellent niche on downland. Dorset and Hampshire are the best counties for the group but Surrey is not far behind and recruitment of new species is better with this group than almost any other as three types of bush-cricket have expanded across the region.

One of our largest crickets, the Wart-biter (Decticus verrucivorus, 35mm), is a species of calcareous grassland and designated as vulnerable, with colonies in East Sussex, Dorset, Wiltshire and Kent (a reintroduction). It is the subject of a Biodiversity Action Plan. Populations tend to be small in most instances, with 50 or fewer adults, and are found on south-facing slopes where eggs are laid in bare soil or short turf and spend two winters underground.

The Wart-biter is declining in much of its European range too. Food includes plants and other invertebrates which stand little chance against such a sizeable species boasting very strong mandibles – the English name comes from the supposed use of the cricket for cosmetic purposes centuries ago.

One of the commonest grasshoppers is the Meadow Grasshopper (Chorthippus parallelus, 18mm), shown on Fragrant Orchid on the previous page. When courting, males follow the usual method of stridulating (rubbing the hind legs against the forewings to make a chirping song) so familiar to anyone who walks across the downs. As can be seen from the image, this may occur very close to the female. All species have a different song.

Meadow grasshoppers, like all others, are herbivores and tend to need longer and damper grassland than some species, as egg-laying occurs only in moist soil. Even so, they are common enough on downland.

Field Grasshoppers (Chorthippus brunneus, 20mm) are exceptional fliers that can take to the air for up to 50 metres. Their colour is variable, with individuals showing straw, buff, brown, green or purple. The song is loud and the female lays eggs only in dry soil including, from my observations in 2004, within a tree root-plate.

One species which is found almost entirely on south-facing calcareous grassland in Britain and is nationally scarce is the Rufous Grasshopper (Gomphocerippus rufus, 15mm). Adults appear relatively late, from August to November in warm years, and they are readily separated from other Orthoptera by having clubbed antennae with a white tip. The North Downs are a stronghold.

One significant distinction between grasshoppers and bush-crickets is the considerable length of the latter's antennae. Another is that male bush-crickets stridulate solely with the forewings. They are partly carnivorous and some are active at night.

The Dark Bush-cricket (Pholidoptera griseoaptera, 22mm) is decidedly common and found in almost every habitat, especially those with brambles or marginal vegetation. They are active during the day and the male has small wings. However, Dark Bush-crickets seem to be less at home in dry chalk areas than an arrival that has been spreading like wildfire and seemingly replacing them in this habitat.

Roesel’s Bush-cricket (Metrioptera roeselii, 18mm), equally chunky though slightly shorter, is the name of this newcomer, which has a very noisy, buzzing song. In 1940 they were restricted in the south to the Thames Estuary but now they are present in virtually all lowland England. A long-winged form is common in hot summers, which helps dispersal of the species. Tall weeds and rough grassland, including on set-aside land, suit it admirably, and with this habitat increasing – an index often of lack of proper management – its prospects of further expansion look good.

The Long-winged Conehead (Conocephalus discolor, 18mm) was first found in England in 1931 and is now widespread, assisted by being able to fly powerfully and breed prodigiously. Strong flight is a disadvantage for individuals if orb-web spiders such as the Cross Spider (Araneus diadematus, body to 15mm) are present in numbers. Another spreading species, the slightly smaller Short-winged Conehead (Conocephalus dorsalis), is less able to cope with dry habitats and hence is not located in so many places.

One shieldbug found almost exclusively on chalk downland is the Tortoise Bug (Eurygaster maura), which is nationally notable. Commoner and found on downland but also in plenty of other habitats is the related Tortoise Bug (Eurygaster testitudinaria, 10mm). A translation of the scientific name is Tortoise-like Fatbelly, not a title likely to endear the insect to the public at large. Unlike its relative, it is increasing in numbers quite dramatically.

Another shieldbug found on downland, though also on heathland, is the tiny Blue Shieldbug (Zicrona caerulea, 7mm), which changes from red to blue as the nymph becomes an adult. They are snappy in action as well as appearance, preying on flea-beetles (Altica sp) as both larvae and adults.

A beetle which is not specific to downland but is ideally suited by the profusion of grass found in that habitat is the Bloody-nosed Beetle (Timarcha tenebricosa, 9mm). Our largest leaf beetle, it is flightless, feeds on bedstraws and herbs and obtains its colloquial name from the habit of releasing a drop of red fluid from the mouth to deter predators when alarmed.

The same comments about habitat apply to the Wasp Spider (Argiope bruennichi, 13mm female), which is a fine mimic that's commonplace in Europe and is increasing its range in Britain, where it was first found in 1922. Males are only about a third of the size and much drabber in colour.

Wasp Spiders live in long grass and low vegetation, including but certainly not exclusively on downland, where females can sometimes readily be seen on the web awaiting the arrival of prey.

They build an orb web with a vertical zigzag pattern of silk called a stabilimentum. The egg sac is constructed on grass stems, which means habitat that is regularly cut is unsuitable. Though protected in Belgium, the Wasp Spider has no such status here.

A wasp that is found more often on downland than anywhere else, in Surrey at least, is Aporus unicolor (10mm), an impressive and nationally scarce spider-hunting wasp that enters the lair of the so-called Purse-web Spider (Atypus affinis). The latter species can live for up to eight years in its undergound silky tubular web, to which Aporus unicolor gains access by using its enlarged fore-femur. Once in, the wasp overpowers the resident, lays an egg on her and promptly leaves the sac in which her progeny develops.

One large invertebrate to have colonised the North Downs and parts of Hertfordshire and the Cotswolds is the mollusc the Roman Snail (Helix pomatia), which is endangered across its European range because of unsustainable collection as a culinary delicacy.

The snail has a shell diameter of up to 50mm, making it by some way our largest. Introduced by the Romans, and by some estate owners in more recent centuries, the escapees have never managed to extend their range significantly. Unfortunately, seemingly they are being collected and sold to restaurants here too, which does not bode well.

Flies, grasshoppers and spiders are the staple diet of Common Lizards (Lacerta vivipara, 13cm), which are just as comfortable on downland as on heathland, possibly more so when there are warm south-facing slopes in which they can bask and hunt.

Images © Jeremy Early. All rights reserved.

My latest book, My Side of the Fence – the Natural History of a Surrey Garden, was published in spring 2013. Details may be found, and orders placed, via this hyperlink My Side of the Fence.

DOWNLAND: Birds . Butterflies . Bees . Other Invertebrates . Flora