8
The Essex Naturalist
Aculeate Hymenoptera, with a number of nationally scarce species. The hill had
been grazed by sheep in the past and has probably always had rabbits. Now it was
grazed by horses. Although the area covered by the old gravel pit was once
arable, I felt sure that the grazed part of the hill had never seen the plough. The
survival of both Autumn Squill and Bluebell would support this. Meadow
Saxifrage Saxifraga granulata which nowadays hardly survives outside old pasture-
land and churchyards was also present. The continuity of grazing has allowed
some scarce insects to survive including the large and now rare robberfly Asilus
crabroniformis. At the time I found two on Broom Hill on 5th September 1991
there had been no records in Essex for fifty years. It now appears that this
magnificent fly is not infrequent in the Tilbury area. This is probably thanks to
the horses, as its large larvae are predatory on the grubs of the dung-feeding Dor
Beetle Geotrupes spiniger which also occurs on the hill.
Tilbury Marshes
The drainage ditches of Tilbury Marsh seem to have been ignored by naturalists
until a survey was carried out by the Nature Conservancy Council in 1987. This
led to the discovery of Groenlandia densa a water weed thought to be extinct in
the county. The survey team also discovered the Water Spider a tiny pondskater
Microvelia pygmaea and two scarce Soldier Flies (Odontomyia tigrina and O.
viridula) amongst several other scarce invertebrates. I visited these marshes on
27th August 1991 prior to cycling to Broom Hill. I was surprised to find the
ditches deep and filled with fresh water. Many were covered with Potamogeton
natans with a submetged flora consisting of Ivy-leaved Duckweed Lemna trisulca,
Curled Pondweed Potamogeton crispus and Horned Pondweed Zannichellia
palustris. The emergent plants included Water Violet Hottonia palustris which
had never been recorded from here. The fauna seemed interesting too with
Ruddy Darter dragonflies Sympetrum sanguineum and even a common lizard was
seen scuttling across the floating pondweed.
Conclusion
Space does not allow mention of other interesting sites such as the remnant
grazing marshes (see Ferry Fields report by P Harvey in Newsletter no. 12) and
the huge area of waste ground east of the Power Station where White
Horehound Marrubium vulgare grows in abundance. Finally, I would like to add a
few oddities to the list of Tilbury rarities.
European Scorpion Euscorpius flavicandis
Apparently, colonies can be found in Tilbury Docks.
Field Cricket Gryllus campestris
There is a 1960s record from the "Tilbury area". Could this extremely rare
insect have once lived here?