I imagine anything that goes wrong when the adult insect is emerging and before the elyptra have hardened could cause blemishes and deformed areas on the elyptra. I imagine emergence in cold weather, damp conditions or other particular factors or happenings during this very vulnerable period could easily cause problems. I recently found a large dead Carabus ground beetle with rudimentary elyptral development, where the expansion of the elyptra had clearly not successfully taken place. This was so severe that the insect had failed to survive. Spiders can also fail to extricate themselves from the old exoskeleton at a moult, resulting in death. In these cases humidity certainly sometimes seems to be a factor.
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The weblog below is for naturalists to use to report interesting sightings, ask questions, report on field meetings and generally post pictures and any information or questions generally relevant in some way to the wildlife and geology of Essex. You will need to register and be logged-on to post to the forum, and you need to upload pictures first, for use in posts. Find out more