134 Essex Specialities. 4: the spider Baryphyma duffeyi
on the head are known to involve mating strategies. In Essex adult males have been collected in
May and females between May and mid July but Merrett (in Bratton 1991) states adults of both
sexes are found from April to June. Subadult males can be recognised in the autumn because they
already possess a partly developed head protuberance. The spider has typically been found in tidal
litter or on mud at the base of vegetation in salt marsh along the sides of tidal rivers and tributaries
of the Stour, Colne, Crouch and Thames (see Fig. 2) and may be abundant locally. The spider has
been found along the Thames as far west as Dartford and Crayford Marshes in Kent and Rainham
Marshes at Purfleet in Essex. B. duffeyi seems to prefer the higher tidal reaches of rivers or their
tributaries and this would repay a proper study to investigate the significance of vegetation struc-
ture, substrate, tidal factors and salinity on distribution. Prey presumably consists of small inverte-
brates but little is known about prey capture or ecology.
Despite fieldwork B. duffeyi has not been found in the Blackwater Estuary, but it seems likely that
populations may occur. Searches in salt marsh and tidal litter should be made, especially in the
Maldon area between Northey Island and the upper reaches of the tidal river. It also seems likely the
spider may occur at some points along the Roach, a region which is under-worked for spiders.
Baryphyma duffeyi has a very restricted distribution in Britain. Most of the known populations are
fragile and exist in extremely localised habitats which are threatened by development, recreational
Figure 2. Baryphyma duffeyi distribution in Essex and the East Thames Corridor
Essex Naturalist (New Series) 17 (2000)