Orthoptera and allied insects of Essex 2003
TIM GARDINER
Centre for Environment & Rural Affairs (CERA), Writtle College,
Lordship Road, Writtle, Chelmsford, CM] 3RR
The author has been monitoring the abundance of grasshoppers al Joyce Field (TL664067) on the
Writtle College Estate since 2000. These surveys allow the abundance of grasshoppers in different
years to be compared, therefore, giving an indication of the effects of weather on Orthoptera. The
study site is unmanagcd grassland dominated by Perennial Rye-grass Lolium perenne and Broad-
leaved Dock Rumex obtusifolius. The monitoring has been conducted by counting the number of
adult individuals of Lesser Marsh Grasshopper Chorthippus albomarginatus and Meadow
Grasshopper Chorthippus parallelus in 10 randomly placed 2x2 metre quadrats once in late July
and again in August (total of 20 quadrats).
Individuals were recorded in each quadrat by brushing the vegetation with a pole to cause any
grasshoppers present to jump (Richards & Waloff 1954). The 'flushing' of grasshoppers was
conducted in a standardised method, ensuring coverage of the whole quadrat by moving from one
edge to the other, sweeping the vegetation in a 180° arc. If a grasshopper jumped out of the quadrat
it was still recorded, however, if a grasshopper leapt into the quadrat from outside, it was not
counted. The surveys were conducted under similar hot and sunny weather conditions, and the
number of individuals counted allowed the density per m2 to be calculated for both species in all
four years.
The 2003 Season
Chorthippus parallelus was most numerous at Joyce Field in 2003 (Fig. 1). The density recorded
for Illis species (0.85 per m2) was more than twice the 2002 figure (0.38 per m2) and seven times
greater than in 2000 (0.11 per m2). Chorthippus albomarginatus abundance was at a similar level
to that recorded in 2001. The remarkable population 'explosion' of the former species in 2003 may
be due to the extremely sunny weather and low rainfall between April-September (Table 1). Increased
solar radiation can lead to faster development of nymphs and earlier maturity (Marshall & Haes
1988). Grasshoppers are particularly vulnerable to predation and disease during their nymphal
stage (Brown 1983), so a reduced maturation time may lead to increased survival and consequently
a high number of adults. The low rainfall retarded grass growth and produced a short and sparse
sward at Joyce Field which may have provided better environmental conditions for diurnal activity
and egg / nymphal development than dense vegetation (Clark 1948; van Wingerden ei al. 1991).
Table 1: Total rainfall and sun hours for the
six month period April-September for 2000-2003
Year Total rainfall (mm) Total sun hours
2000 346.5 1002.2
2001 384.3 1192.9
2002 272.0 1094.3
2003 181.3 1289.9
Data from the Writtle College Weather Station
Essex Naturalist (New Series) 21 (2004)
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