In the heathland around Bruges you can hear grasshoppers again. Their comeback means that recreating heathland pays off.
Around 1775 the north of West Flanders still had 9,000 hectares of heathland. That’s more than twice as much as the famous Kalmthout heath (north of Antwerp) today. In 2002 only 38 hectares remained between Jabbeke and Aalter. But today the heathland around Bruges is being extensively restored: by digging off pieces and letting sheep graze there. In this way trees and grasses can’t dominate the landscape.
Today, the bell heather (Erica cinerea), cross-leaved heath (Erica tetralix) and common heather (Calluna vulgaris) are back, and expanding. And the typical heather insects, such as grasshoppers and field crickets also benefit from it, entomologists and collaborators of the Royal Belgian Institute of Natural Sciences (RBINS) are noting.
They have been sampling the Bruges heathlands intensively for insects since 2014. Insect traps were placed on 40 sites in 15 different heathland areas. These are emptied every two weeks with the help of volunteers. These traps sometimes contain unexpected guests that have never been spotted in Belgium before: among others the centipede Geophilus easoni and three species of shore flies (of the Ephydridae family).
More Grasshopper Species
In 2018 we found fifteen grasshopper species in the insect traps, eight of which are indicator species of the heathland’s quality,' says RBINS’ entomologist and project leader Wouter Dekoninck. For the sake of completeness: mottled grasshopper (Myrmeleotettix maculatus), the meadow grasshopper (Pseudochorthippus parallelus), the lesser mottled grasshopper (Stenobothrus stigmaticus), the slender ground-hopper (Tetrix subulata), the lesser marsh grasshopper (Chorthippus albomarginatus), the bow-winged grasshopper (Chorthippus biguttulus), the common field grasshopper (Chorthippus brunneus) and Chorthippus mollis.
In a few places in the Beisbroek nature reserve, sampling took place long enough to detect clear changes in grasshopper populations. At the beginning, in 2014, only the common ground-hopper (Tetrix undulata) was found. Six years later, the diversity has increased fivefold!
And that’s probably an underestimate. The grasshoppers are a bycatch in the bottom traps - buried glass jars - ideal for catching bottom crawlers. But the more mobile grasshoppers often live higher up in the crops. “With nets that collaborators drag over the ground and vegetation, we hope to be able to detect grasshoppers even better in the future”, says Dekoninck.
“By the way, we are also looking for the ‘golden grasshopper’ (Chrysochraon dispar, not an indicator species). It has already been spotted south of the Tillegem nature reserve, and heard in the nature reserve itself, but we couldn't get our hands on it yet. Auditory observations are valuable, but we have to be careful. The sound of the golden grasshopper for example is difficult to distinguish from that of the meadow grasshopper (Pseudochorthippus parallelus).”
Field Cricket: Reintroduced?
A surprise in recent years: the return of the field cricket (Gryllus campestris). This cricket used to be everywhere in heathlands but due to intensive farming from the 20th century onwards, the population in Flanders declined sharply. Today, the populations are very small and fragmented.
In 2016, the field cricket was spotted again in the Bruges heathland, in the Schobbejakshoogte nature reserve. “Our monitoring shows that the population is doing quite well. Nymphs (young individuals) of the field cricket have been found in nearby areas. That suggests the species is expanding.”
“Since the field cricket had been extinct in the Bruges area for decades, we suspect that the new population was reintroduced. The field cricket does boost local insect diversity, but is such a reintroduction the right method? The new population will probably have no genetic relationship with the original population of that area.”
Connecting Isolated Patches
The established diversity of grasshoppers tells us that heathland recovery and management around Bruges is going in the right direction. Dekoninck: “It will be important to keep up the efforts, and also to choose the right areas to recreate heathland. Our research also shows that there are less grasshoppers in heathland patches that are 'surrounded' by forest, isolated from other heathland areas. It is difficult for the insects to migrate from the open heathland to these isolated areas. We must try to connect them, and also avoid them being intersected by motorways.”
The study was the subject of the thesis by Yuri Walscharts (Hogeschool Gent).
