Jimmy McKellar
Introduction
In general spiders are not a good group to record without taking a specimen as the major identification features only show up under a microscope. However there are always exceptions and Nuctenea umbratica is one of the few that can be reliably identified by sight alone.
Identification
Both males and females are of a dark brown to black colour with at least 4 and sometimes even 6 noticeable depressions on their backs (see picture). They are also dorso-ventrally flattened to allow them to slip into gaps in wood or behind bark on trees. Specimens I have examined have a couple of white patches on the underside and I suspect all specimens do. Both sexes have a row of 4 white dots down each flank of the abdomen though this can be less evident, or possibly even absent, in lighter specimens.
Nuctenea umbratica photographed at night 15 Oct 2005, Scorguie.
Photo © Jimmy McKellar
Distribution of Nuctenea umbratica in Highland. Red - HBRG records; green - additional records from NBN Gateway, 20 Oct 2005.
Distribution, Phenology, and Life Cycle
In the Provisional Atlas of British Spiders by Peter R. Harvey, David R. Nellist and Mark G. Telfer, the status is described as common, but the distribution map shows only a handful of records for Highland.
I recently sent out a request for records to a small group of recorders and have already received records to fill in a few of the gaps, so with a little effort I feel sure we can make a huge contribution to the distribution map. The map now clearly shows the contribution HBRG has already made by extending coverage to the north into Easter Ross and beyond.
They are said to normally appear between late spring and autumn but as they are nocturnal this probably accounts for the paucity of records. However they are also synanthropic, which gives us the chance to target this species without travelling. If we ask group members and others to go out and check the outside of their sheds and fences with a torch we would probably get good results. Edward Milner advises that one other place to look is on dead trees or dead branches of live trees, where they often seem to spin their orb-webs.
I believe females occasionally overwinter and less commonly so do males. On 5 February 2005, David W. McAllister found six around his garage, which adds weight to the theory that at least females overwinter as sub-adults rather than as eggs. The female I saw in February 2005 was not large by the species standard. This reinforces the theory that they are sub-adult during the winter. Measured from the front of the carapace to rear end of abdomen my specimen male was 8mm, which is the correct size for a mature adult. (Males 8-9mm; females 11-14mm). This left me with the impression that these would have been hatchlings of the previous year, and assuming the female on my shed is the same one (and I have no reason to think otherwise) females appear to take a year to mature. This leaves us with a couple of unanswered questions. Just when do these spiders mature and appear? And where and when do they lay their eggs?
Behaviour
I looked for a particular male but was unable to see where it could be hiding during the day. Later, when shining a torch on it I was able to follow it to its retreat. It slid into a crevice after making three 90° turns so that it was behind a strap on the shed and several inches from its normal spot. Little wonder I was unable to find it.
I discovered that when I shone a torch on them they go into hiding, as you would expect with a nocturnal species. Nuctenea umbratica is a member of the family Araneidae so spins an orb web, though the web can be difficult to see on occasions and at first I suspected my male did not even have one.
These are interesting spiders and by concentrating on just this one species I have discovered quite a lot in a short time, if you have any comments or observations to make please feel free to email me including your address, date of record, place (with six figure grid reference), altitude, and any other useful details.
