Pedilus lugubris is one tiny beetle, only 5mm

Male pyrochroid beetles are known to climb onto blister beetles and ingest the cantharidin exuded by the insect. Completely immune to the effects of the blistering agent, they use the chemical to attract females, who become the recipients of a cantharidin-laden sperm packet with which they coat their eggs.

There are also other insects that eat live or dead blister beetles to obtain the protective qualities of this chemical defense; these are all called cantharidinophilous, as in "cantharidin lover."  I assume they use the chemical in similar wise; passing it to their female cohorts. 

The poisonous substance cantharidin is comparable to cyanide and strychnine in toxicity. Stored in the insects' blood, it is very stable and remains toxic even in dead beetles. Animals may be poisoned by ingesting beetles while grazing or eating harvested silage. Horses are particularly susceptible to cantharidin poisoning. Externally, cantharidin causes severe skin inflammation and blisters.

In animals, cantharidin is absorbed through the intestine and can cause symptoms such as inflammation, colic, elevated temperature, depression, increased heart rate and respiration, dehydration, sweating, and diarrhea. There is frequent urination during the first 24 hours after ingestion, accompanied by inflammation of the urinary tract. This irritation may also result in secondary infection and bleeding.  Taken internally, as little as 10 milligrams can be fatal in humans.

The concentration of cantharidin in adult beetles depends primarily on the sex; males produce the chemical and only pass on small amounts to the females during mating. Cantharidin amounts also depend on species; the striped blister beetle has approximately five times more catharidin than the black variety. In one species, Méloé proscarabaeus, cantharidin makes up fully 1/4 of the insect's blood. [1] [2]