July 2019

Yesterday I saw two swifts.  It is only the second time I have seen swifts this year, the worst year since we moved here.  Swifts are in serious decline as highlighted on BBC’s Springwatch recently.  They suggested that part of the reason for the lack of swifts this year has been bad weather in Spain that has delayed or interrupted their migration.  Another reason for their decline is the dramatic decline in the number of insects.  Swifts feed exclusively on flying insects and stay on the wing throughout their lives except for brief periods to mate and nest.  Martins and swallows also feed on the wing, but they do land to roost as well as to nest and mate.  Their ability to land may also allow them to pick off crawling insects to supplement their diet, something swifts cannot do as they have no claws that would enable them to grip a perch.  Another difference is that swifts tend to fly much higher than swallows or martins when they feed but it’s debatable whether that is a factor in their decline or not.  It will be a sad summer when swifts no longer reach the UK, and that summer doesn’t seem that far away.

I found out something interesting about the bee-wolf (Philanthus triangulum) recently.  The bee-wolf is a solitary wasp – solitary because it doesn’t form a colony like the more familiar social wasps that will ruin your picnic – and is one of a group called digger wasps.  It digs a long burrow in soft sandy soil and will dig brood chambers at intervals along the burrow.  It then goes out and catches honeybees which it paralyzes with its sting and then carries the bee back to its burrow.  It will do that three or four times for each chamber and will then lay a single egg in each chamber.  Note that the honeybees are only paralyzed, not dead because they stay fresher like that.  The egg then hatches and the larva feeds on the paralyzed honeybees – yes, it’s gruesome!  It has been estimated that a typical beewolf burrow will contain up to a hundred honeybees.

Bee-wolf - Philanthus triangulum

I have been reading about the relationships between insects and bacteria recently and how insects use bacteria to aid digestion, and about how bacteria affect the behaviour of insects.  The interesting thing about the bee-wolf is that it can exude a white paste from its antennae which contains a particular strain of bacteria.  The bee-wolf daubs this paste onto the roof of the burrow.  This has two purposes – firstly, it shows which way is out when the next generation emerges from their chambers the following year, and secondly, it passes on that same strain of bacteria to the next generation for daubing on to their burrows.  Bee-wolves are active from July to September and should you wish to see them in action, I can recommend the RSPB Nature Reserve at Dungeness.  There is an area of sandy soil on the right of the track about 50 yards before the visitor’s centre where you can see bee-wolves carrying their prey to their burrows and you can marvel at their strength and their gruesome lifestyle.  Don’t worry about being stung – they are only interested in bees.

Bee-wolf with prey -  you can just see the outline of the bee below the wasp

Incidentally, the bee-wolf used to be a rarity in Britain until the late 1980’s.  They have since expanded their range considerably and are now commonly seen throughout the south and east of the country.  They are common in continental Europe and are known to expand their range during long hot summers.  I guess I could bang on about global warming now but I won’t – maybe next month.