Yellow Legged Asian Hornet
Methods of monitoring
Hornet foraging activity can be monitored using traps or monitoring stations. Traps are composed of
an enclosure with a bait for attracting yellow-legged hornets. As the bait will also attract other
invertebrates, traps should only be used if they have the means to allow non target invertebrates to
escape, and to prevent entry of the larger, native European hornet (Vespa Crabro). As some
beneficial insect populations in the UK are in decline, we strongly urge that only traps that do not
harm non-target invertebrates are used.
Monitoring stations are composed of an open tray or container with a bait, or a closed jar or container
with a bait, and a wick. This allows invertebrates and yellow-legged hornets, if present, to visit the
station to feed and fly away. It has the benefit that non-target insects are not harmed, and the
trajectory of the hornet’s return to its nest can be determined. Monitoring stations are used by NBU
Inspectors during active surveillance for yellow-legged hornets. The disadvantage is that they require
active monitoring.
Monitoring traps
Traps can be home made, or purchased from various retailers. It is important to use traps that have
been designed with openings of different sizes. This allows entry of invertebrates the size of the
yellow-legged hornet or smaller, thereby preventing entry of large native hornets; but with escape
apertures small enough to allow the smaller, non-target invertebrates to escape once inside; but too
small for the yellow-legged hornet to escape. The commercially available traps vary in how selective
they are at catching yellow-legged hornets. It is important to note that yellow-legged hornet queens
are larger and wider than workers; queens are up to 30 mm long, but workers are up to 25 mm. Here
we mention a small number of non-lethal, selective traps that have been used in the field by National
Bee Unit (NBU) Inspectors.
The Gard’Apis trap (Fig 1a) is a selective and non-lethal trap that comes with two different nozzles;
one (in red) for catching yellow-legged hornet queens in spring and the other (in orange) which is
narrower, and used for catching workers from May onwards. Both nozzles prevent European hornets
from being accidentally captured, and the mesh on the sides of the trap allow smaller insects to
escape. A small dish inside is used to hold the bait.
The Asian hornet trap (blue/yellow) by Andermatt (Fig 1b) is a selective, non-lethal trap for yellow-
legged hornet monitoring. The trap has 8 mm entrance holes that are large enough to allow the
yellow-legged hornet, and any smaller invertebrates, into the trap. However, the entrance also has a
5 mm groove which allows the smaller invertebrates to escape. A yellow platform placed above the
bait prevents the inhabitants from drowning, and makes the trap non lethal.
The Ornetin Asian hornet trap (Fig 1c) is designed as a lid that screws onto a 100 mm diameter jar
(not supplied). The lid is screwed onto the jar, which is placed on its side with a small bundle of straw
or cotton soaked with bait, but not so much that liquid pools in the trap. The lid has holes large
enough to allow the smaller invertebrates to escape, while keeping yellow-legged hornets trapped.
Please avoid use of lethal traps, without modification, as they may harm native invertebrates, and
sticky/glue traps, which may harm birds. Please monitor traps regularly, especially when testing a
new trap, to ensure that non-targets can escape, and if they cannot, release them, and check to
ensure that traps have not filled the rainwater, potentially drowning the occupants.
If you wish to construct your own trap, there are pre-made trap openings called ‘ferrules’ (Fig 1d) that
can be purchased and installed in home-made traps. Alternatively, there are many patterns for 3D
printing. Use of these will help prevent the capture of non-target invertebrates. Home-made traps
should also contain a platform or wick, to prevent invertebrates from drowning in the bait.
Monitoring stations
To set up a monitoring station, place a dish or container in a sunny, visible location with a small
amount of bait or attractant on it. If necessary, place a wick or some straw over the bait so that
invertebrates do not drown in it. Check the monitoring station at regular intervals throughout the day.
Please note that while it is not legal for members of the public to capture and release yellow legged
hornets, monitoring their foraging activity is permitted.
Monitoring using a ‘monitoring station’ is unlikely to be informative in spring, when only queen
hornets are likely to be foraging; chances of encountering one with this method are low, so
‘monitoring traps’ are preferred. Monitoring stations are more appropriate for use in the mid season,
especially during August, when hornet foraging will be at its peak. NBU Inspectors use monitoring
stations when hornets are known to be in the area. They use the stations to visually monitor for
foraging hornets, and observe the trajectory of the hornets after feeding, as they return to their nest.
In this way, they have been successful at tracking and tracing hornet nests. We recommend the use
of monitoring stations when hornets have been reported in the surrounding area. When observing the
monitoring stations, it will be helpful to have a camera nearby to photograph any suspect hornets.
Where should I monitor?
The yellow-legged hornet could arrive anywhere in the UK. Monitoring is especially important if you
live close to a ‘risk point’ such as a ferry terminal or port, and in regions where hornet nests have
been discovered in previous years. We would encourage everyone in high-risk areas to monitor
regularly, especially if there is an alert from the NBU and BBKA warning of a nearby incursion. There
is no need for spring monitoring in areas that are not at high risk.
Monitoring stations and traps are best placed in sunny areas; in trees, on hive stands, in and around
affected apiaries, and at head height. Avoid placing them in shaded areas, as hornets are less likely
to forage there.
When should I monitor?
Yellow-legged hornet queens emerge in early spring, traps for queen trapping can be placed from
March until May. For spring monitoring, traps are more appropriate than monitoring stations. yellow-
legged hornet workers forage throughout the beekeeping season, so monitoring should continue from
spring until autumn. For post-spring monitoring, traps or monitoring stations can be used.
Which bait should I use?
Sweet baits are highly attractive to foraging yellow-legged hornet queens in early spring. This is
because queens emerging from hibernation need high-energy, sweet foods. There are many
variations of home-made sugar baits, these include mixes of sugar and various types of dark beer,
alcohol or fruit juice.
During the summer, worker hornets forage for protein sources to feed the larvae. To make a protein
bait, raw meat or fish with water can be used. The NBU have used protein baits consisting of mashed
fish or prawns, diluted to 25% in water. If you choose to use a protein bait, it will need changing after
3 days due to decay and an unpleasant aroma. Yellow Legged Asian Hornets also feed on windfall
and ripe fruit. This can be used as bait later in the season.
NBU Inspectors use a commercially available wasp bait called Trappit (Suterra) for track and trace. It
is a sweet bait that contains a bee deterrent, and can be used throughout the year, as hornets always
need to feed on sugars for energy. Other wasp baits are available.
How do I empty monitoring traps?
Release all other live, native insects to preserve as many non-target species as possible. Traps
should be visited and emptied regularly; ideally daily. It is very important not to harm native
invertebrates.
Please take care when releasing insects if stinging insects are present in the trap. Hornets and
wasps can sting and can cause a severe reaction. Most insects are not naturally aggressive but can
be defensive when trapped. If you are concerned about releasing stinging insects, the traps can be
chilled down in a fridge for about 30 minutes or until they slow down. Empty the trap somewhere
warm and dry outside, and the insects will eventually wake up and fly away.
If you think you have caught a yellow-legged hornet, you can place the whole trap, unopened, in a
sealed freezer bag. Place the bag containing the trap into a freezer for 12 hours before opening, to
avoid being stung or losing your suspect specimen. Alternatively, traps can be placed into a bucket of
soapy water for an hour so that the hornet can be safely sieved out.
How do I know if I have caught a Yellow Legged
Asian Hornet?
There are thousands of misidentifications in reports for yellow-legged hornet every year. These
reports can be time-consuming to follow up. We would therefore request, before submitting a report,
that all individuals familiarise themselves with what the yellow-legged hornet looks like, and how to
differentiate it from native invertebrate species. Full guidance on identification can be found in the
Yellow Legged Asian Hornet identification sheet.
Conwy Beekeepers would like to acknowledge and thank the National Bee Unit for the above
information.