METOECUS PARADOXUS (L)
Harry Green
On the 2nd August 2002 I received an email from Sarah Price of
Oldham (greater Manchester) who said that the local council had
recently found Metoecus paradoxus in her roof. She
wanted to know if it was a rare species and should she be excited
about the discovery! Quite why she had contacted me I do not know
but guess it was through some internet loop via our web site www.wbrc.org.uk.
At the time I knew next to nothing about this beetle but soon
discovered it was a parasite of underground wasps' nests. Wishing
to learn more I place a query at the coleopterist e-group and
received several very useful responses which led to useful
literature (see references).
Metoecus paradoxus was known as a beetle for 130 years
before its life-cycle was understood. Elucidation caused vigorous
argument and controversy amongst Victorian naturalists in the
1860s and 1870's. The development of the larvae in wasps' nests
was described by Chapman in 1870 and he finally obtained the
missing information in 1890on how the larvae entered the nests (reference
list in Edwards 1980). To date I have seen no recent reports of
study of the species - most texts repeat earlier observations -
which is what I am doing in this article! The life history is
reminiscent of that of oil beetles.
The beetle itself is a rather odd-looking almost fly-like insect
about 10 mms long with narrow pointed elytra which do not
completely cover the wings or abdomen. The larva is first an
internal parasite of a wasp larva, soon emerging and wrapping
round the larva as an external parasite sucking body fluids from
its victim before finally eating the lot! After pupation the
beetles emerge and leave the wasps' nest. The part of the cycle
which took so long to discover is that the female lays her eggs
on rotting wood in the autumn which is likely to be visited by
wasps in the following spring when they seeks wood to chew and
convert to nest-building paper. The first larva is a triungulinid
about 0.5-0.75 mms long with long legs provided with suckers. The
larva hatches in early summer and waits on the wood for a worker
wasp to visit. The larva climbs on to the wasp and is carried
back to the nest where it actively searches for a cell with a
half-grown larvae which it parasitizes. The beetle larva grows
rapidly, pupates, and the beetle emerges about 2 days after a
wasp should have done.
The early reports and texts suggest that Metoecus
parasitizes underground nests primarily of Common Wasp Vespula
vulgaris, and sometimes Vespula germanica. The
modern reports I have seen by Ives 1991, 1992 and Gillett 1992
reported the beetle emerging from wasps' nests in roof spaces or
other parts of buildings, and of course the email which started
me on the trail referred to a nest in a roof space.
Interestingly, it turned out that the Oldham occurrence had been
referred by Environmental Health to a coleopterist and comment
came back to me via another internet loop - the coleopterist e-group!
This group also produced a report from Warwickshire with records
from 11 sites, and five of those from domestic premises, and
mention of near-moribund adults on a first floor windowsill.
Apparently my old friend Roger Juckes had reported 150 emerging
from a crevice next to a central heating pipe after two wasps'
nests had been destroyed.
The climax of this story came first as a phone message to the
Worcs Wildlife Trust Office on 3rd September from Jean Osborne,
Selly Oak, Birmingham. "She had got Metoecus paradoxus
in her greenhouse - was I interested"! Well, Yes, I was!
After contacting her she sent me a few beetles and also wasps to
identify - Vespula vulgaris - and the following summary
(dated 24th September 2002:
1. Our house is a dormer bungalow as we had a sitting room put in
the roof space when we bought it 26 years ago.
2. We tend to get a wasp nest in the roof space almost every
year, but live in mutual harmony most of the time.
3. This year the nest is above the kitchen and because of the
adjoining lean-to greenhouse some of the wasps exit through the
greenhouse while others enter above the greenhouse.
4. If we had beetles previous years we would not have noticed
them, but because they turned up on the greenhouse windowsill
they did come to my notice, though initially I didn't realise
where they were coming from and thought they were something to do
with our ring culture tomatoes.
5. I sent a beetle to Roy Ledbury, President of Birmingham
Natural History Society, when it dawned on me that they were
beetles and he said that he thought it was Metoecus paradoxus but
it couldn't be as they were associated with underground wasp
nests! I had not told him about the wasps.
6. Beetle numbers. They are now not appearing every morning, but
for about 6 weeks we were tipping ten to a dozen out through the
greenhouse door each morning, some got tied up with plant pots on
the windowsill and died but they were quite numerous.
7. We have various plant pots standing on old tree stumps on our
patio and some of this wood is getting soft and rotten while our
compost heaps up the garden have wood sides that we have to
replace as they rot every few years, so there is a source of dead
wood available, but how do they know to use it?
Following this I calculate that at lease 500 Metoecus
paradoxus must have emerged from a wasps' nest in her roof!
Worcestershire records.
We have very few local records. One was found in Worcester two
years ago, and whilst on an invertebrate foray near Birtsmorton
24th July 2002 John Meiklejohn collected one in his net when
sweeping tall vegetation well away from buildings.
The RECORDER 3.3 database describes the species as widely
distributed but very local. They must easily be overlooked unless
you happen to have a parasitised wasps' nest in your roof! Please
keep a look-out for these curious beetles and let us know if you
find any.
Acknowledgements
Very many thanks to Sarah Price and Jean Osborne for starting and
finishing this trail! Also to participants in the Coleopterist
egroup for useful advice, especially to Matthew Smith who told me
of the very useful publication in the Rentokill Library and
kindly sent me a photocopy of the section on Metoecus paradoxus.
References
BILY S A. 1990. A colour guide to beetles pages 172-173.
Treasure Press
EDWARDS R. 1980 Social wasps, their biology and control.
Pages 151-155. Rentokill Library Series
GILLETT MTP. 1992 Metoecus paradoxus (L) (Rhipiphoridae)
More parts to the puzzle. Coleopterist 1:4-5
IVES E. 1991 Metoecus paradoxus (L) (Rhipiphoridae) A
puzzle. Coleopterist's Newsletter nos. 44 & 45:9-10
IVES E. 1992 Metoecus paradoxus (L) (Rhipiphoridae) A
further note. Coleopterist. 1:17.
LINSSEN EF. Beetles of the British Isles. Pages 92-93.
Frederick Warne
STEP E. 1946. Bees, wasps, ants and allied insects.
Pages 40-41. Frederick Warne.
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