I couldn’t find that story online. I don’t think it’s true.
Here are some British assassin bugs:
They are not poisonous – that is, a cow wouldn’t die from eating one.
But they are venomous – that is, they inject deadly digestive saliva
into their prey – but their prey is other insects, and even if they can kill an insect bigger than themselves, a cow wouldn’t die if it was bitten by one.
Few insects are venomous, and those that are, won’t kill a cow, at least, not on their own. [A big swarm of bees could kill just about anything that didn’t run away, I think, and the same with a colony of army ants.]
Some spiders are deadly, like the Black Widow spider:
Some scorpions are deadly, like the Fat-tailed Scorpion:
Some jelly fish are deadly:
I don’t think any insects are deadly.
What insect stings are, is painful. How painful? You measure the pain of an insect sting according the Schmidt Index, named after a man who having been stung hundreds of times in his career as an entomologist decided to write some notes on it.
According to his scale, the very worst stings of all are the stings of the bullet ant. Also very painful is being stung by a velvet ant (a type of wasp). The sting of a velvet ant is so painful that it is nicknamed the ‘cow killer’, as the sting is so painful that it was supposed it would kill a cow. It didn’t kill Schmidt and I don’t think one has ever killed a cow, but that might be where the assassin bug story got started.
But there is one way an assassin bug bite could kill a cow. Insects that carry diseases can be deadly. I think the Anopheles mosquitos that carry malaria have killed more people than died in all the wars since recorded history. Still do, millions every year. And so tsetse flies and other insects that carry diseases of cattle, can kill a cow that way.
I mentioned Sir Vincent B Wigglesworth:
who studied a bug called Rhodnius. Rhodnius is an assassin bug http://en.wikipedia.org/wiki/Rhodnius_prolixus
It feeds mostly on armidillos, but it can bite humans, and when it does, it can give them Chagas’ Disease, and you can die of it. In fact, these bugs can give Chagas’ Disease to about 150 different animals. So if a Rhodnius bit a cow and the cow later died of Chagas’ Disease, then maybe you could say that a cow died because it was bitten by an assassin bug. But it can take 10-20 years to get Chagas’ Disease…