17 September 2018

You may be wondering how Jersey beekeepers have worked out the distance they are from an Asian Hornet's nest by timing how long it takes a hornet to fly from bait to nest and back? Well it all goes back to elementary mathematics.....

Speed is a measure of how quickly an object moves from one place to another. It is equal to the distance traveled divided by the time. It is possible to find any of these three values using the other two.

So you know the time it takes to go back and forth from the bait and you have a guesstimate of the time at the nest which is considered a constant.  Divide the result by 2. Then use an estimate of the speed of flight of the Asian Hornet and you can work out the distance to the nest. So distance = speed x time

At the moment, the estimate of speed of flight of the Asian Hornet being used is 100 metres per minute or 1.7 meters per second. 

This is what works best to get them closest to the nest they are hunting. The other thing they do is that they take readings at two other bait stations and combine them to triangulate their readings. 

 

Another test of speed 

At the end of August, Jersey Beekeepers carried out another test of speed of flight. Using 3 bait stations with line of sight to a known nest and at a known distance. The length of absence from the bait of marked individual hornets was recorded at each site and, using a hoist with beekeepers suspended above the nest, the time at the nest also. 

This produced a calculation of the flight speed at approximately 3.5 metres per second. 

Bob Hogge, who you can see below being attacked by hornets from that nest, said: 

"Interestingly, the time individuals spent on the nest seemed to be constant at approximately 50 seconds, but this is anomalous with observations from other nests so needs more work as do all the other metrics."



Erratic flight paths 

It's been noticed that hornets do not necessarily use exactly the same path to and from a bait station. In her blog about Hunting Asian Hornets on Jersey, Torbay beekeeper Judith Norman, noted the following habits of the Asian Hornet (you can read the full blog here) : 

"In an open area, they may well fly along a hedge line; in town they may follow open streets! Some may fly straight through a line of trees but others may go all the way around the line of trees. It is easy to see one fly if it has open sky as a background, but, as soon as it passes in front of a tree, for instance, it is no longer visible.

"Having several people with radios cuts down enormously on the time and leg work. If the person at the bait station gives a shout as the insect takes off, the others further down may just manage to get a glimpse of it as it rounds a corner and one can then decide where to place the next bait station in the bid to get closer to the nest."

Determining Sex 

In France the Association Action Anti Frelon Asiatique ( Association Action against Asian Hornets) has identified several ways to tell a male from a female AH. 

There is a difference in size - 2.3 cm for the males on the left and also they are pointing out the two yellow dots on the underneath side of the abdomen which males have and females do not. 

Female antenna are straight but males are curved.  10 rings on the antenna of a female,   11 rings if it is a male.  

Females have a sting, males do not. 

Jersey beekeepers who have dissected many of the 40 or so nests they have found say the only way of telling a Queen from a worker is by the width of the thorax. 

-ends-