Orthoptera and allied insects of Essex 2002
three years are presented in Table 1. These data were obtained from the Writtle College Weather
Station.
The sunniest, yet wettest, weather was recorded during 2001 when both Chorthippus species were
most numerous (Fig. 1). Therefore, rainfall docs not seem to have a detrimental effect on instar
development, but 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 longer maturation time may lead to increased mortality
and consequently a reduced number of adults.
Fig. 1: Density per m2 of adults of two Chorthippus species at Joyce Field
Table 1: Total rainfall and sun hours for the six month period April-September for 2000-2002
Phenology
In addition to recording the abundance of two Chorthippus species, the author noted down the first
and last date that the stridulation (or song) of four common Orthoptera species was heard on the
Writtle College estate during 2002. Mature male adults sing to attract females for mating (Baldock
2000). Therefore, recording the dates of the first and last stridulation heard provides useful data on
the speed of nymphal development. Orthoptera may be a useful indicator of climate change (Burton
2001), as warmer weather during May and June may lead to earlier maturity.
C. parallelus was heard singing at Writtle on 25th June and had a very long adult season of 103 days
Essex Naturalist (New Series) 20 (2003)
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