Posted by: lensweb | August 15, 2017

The Sound of Grasshoppers

Aug 14 Monday Bush Cricket Hunt Bring your bat detector!

Darley and Nutwood Local Nature Reserve

Meet 2:30 at South Avenue entrance

Sat nav DE22 1DZ.

Leader Felicity Jackson

The chirping of grasshoppers and crickets is one of the quintessential sounds of summer. Their song is very unusual in the insect world. At Darley and Nutwood Local Nature Reserve a small group met up with Felicity Jackson who has made a special study of these insects.

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The Darley and Nutwood Local Nature Reserve is based on an old landfill site which was closed and sealed in 1985 and was originally the site of a swan pond of a grand hall. The ruin of a garden temple survives. It is close to the River Derwent and also incorporates a fragment of ancient woodland. Chairman of the management team Dr Keith Dodd explained that the site is fenced so that it can be grazed by sheep and cattle in the winter months.

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Leading us to an area of long grass, Felicity explained that the Orthoptera are an order of insects that have enlarged hind legs for jumping. There are two sub-orders, consisting of 27 native species, the grasshoppers and the crickets.

Crickets have long antennae, grasshoppers have short antennae.

Crickets stridulate by rubbing their wings together, grasshoppers have a series of pegs on the hind legs that produce sound when rubbed against wing veins.  On hot days they can be heard over considerable distances, but in duller weather can be less conspicuous and may be more reliably heard with a bat detector to amplify the sound.

Males can produce up to five songs during courtship: normal song, courtship song, assault song, copulation song and the rivals’ duet

The male sperm is transferred in a package called the spermatophore.

Adult females lay eggs through ovipositors adapted for laying eggs, singly or in pods, into the ground  or base of grasses. Eggs are the overwintering stage.

The immature stages (called nymphs) closely resemble the adults. They hatch in spring when the temperature is suitable for development and succulent vegetation is abundant. Some bush-crickets are predatory and consume grasshoppers or younger stages of their own species.

The number of nymphal instars varies between species but most Grasshoppers have four nymphal instars and most Bush crickets have five or six.

Development takes about two months and the adults usually emerge in July.

Grasshoppers and crickets rely on external sources of heat to raise their body temperature so are reliant on environmental conditions. As they are highly mobile, they may be valuable indicators of climate change.

We set our bat detectors to 22KHz and soon picked up the loud churring of Roesel’s Bush Cricket. We had to look very carefully among the long grass and meadow vetchling before we spotted the actual cricket. We heard about 4 of these before we sighted a wingless bright green cricket with a black stripe down it’s back, this was the nymph of a long winged conehead. After some time we heard an adult male conehead. Through a bat detector, the stridulation is a chugging train engine sound which distinguishes it from the raspberry buzz of Roesel’s Bush-cricket, and from the softer sewing machine stridulation of the grasshoppers.

Long-winged Coneheads (Conocephalus discolor) have been expanding into new territories, with rising temperatures under climate change a likely factor. Roesel’s Bush Cricket (Metrioptera roeselii) is also expanding it’s range. Of course, 21st century records may sometimes reflect the increased use of bat detectors by recorders, rather than range expansion.

Many colour forms exist of Lesser Marsh Grasshopper Chorthippus albomarginatus. It may be a uniform straw brown or dark green with a white line running along the forewing. Fully winged, the side keels of the pronotum are straight which together with a median keel form three parallel lines across the pronotum. We found several females before we heard the soft purring trill of an unseen male which was then tracked to halfway up a plant stem.

The Lesser Marsh Grasshopper can be confused with the meadow grasshopper Chorthippus parallelus or the common green grasshopper but the songs are quite distinct. Meadow Grasshopper has a short rattling song of 1 – 2 seconds duration sometimes described as a dry chuckle of 10 —15 pulses. The Common Green Grasshopper  Omocestus viridulus has a loud continuous song lasting up to 15 seconds. It is soft in tone but far carrying, rather like the sound of hands being briskly rubbed together. Only the Lesser Marsh Grasshopper has been found at Darley and Nutwood so far.

 

Two groundhoppers which are like diminutive grasshoppers have been found on site the Slender Groundhopper Tetrix subulata in which the pronotum extends beyond the tip of the abdomen, giving a characteristic kite shape when viewed from above and the Common Groundhopper Tetrix undulata in which the pronotum is shorter. Their antennae are short and they have no stridulation, courtship being a series of bows.

Felicity was keen to survey the site for speckled bush crickets which have an abrupt, high pitched click, as they are present at nearby Allestree Park, but she was unlucky on this occasion. We were tempted to settle for the night and listen out for the crickets as we watched the Perseids display but – enough!

Pleased to have unravelled the mysteries of grasshoppers singing we were now able to look at other insects. Honey bees and red tailed bees busy on knapweed.  Drone flies, sun flies and even a large Volucella inanis on angelica. Ladybirds, harlequin, seven spot, clown faced (14 spot) and 22 spot.

 

A shining domed black dor beetle with purple under garments was set to work rolling rabbit currants before we left the site.

Marion Bryce 14 August 2017


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