Sir Thomas Browne tells us, in Pseudodoxia Epidemica:

There is found in the Summer a kind of Spider called a Tainct, of a red colour, and so little of body that ten of the largest will hardly outway a grain; this by Country people is accounted a deadly poison unto Cows and Horses; who, if they suddenly die, and swell thereon, ascribe their death hereto, and will commonly say, they have licked a Tainct. Now to satisfie the doubts of men we have called this tradition unto experiment; we have given hereof unto Dogs, Chickens, Calves and Horses, and not in the singular in number; yet never could find the least disturbance ensue. There must be therefore other causes enquired of the sudden death and swelling of cattle; and perhaps this insect is mistaken, and unjustly accused for some other. For some there are which from elder times have been observed pernicious unto cattle, as the Buprestis or Burstcow, the Pityocampe or Eruca Pinnum, by Dioscorides, Galen and Ætius, the Staphilinus described by Aristotle and others, or those red Phalangious Spiders like Cantharides mentioned by Muffetus. Now although the animal may be mistaken and the opinion also false, yet in the ground and reason which makes men most to doubt the verity hereof, there may be truth enough, that is, the inconsiderable quantity of this insect. For that a poison cannot destroy in so small a bulk; we have no reason to affirm. For if as Leo Africanus reporteth, the tenth part of a grain of the poison of Nubia, will dispatch a man in two hours; if the bite of a Viper and sting of a Scorpion, is not conceived to impart so much; if the bite of an Asp will kill within an hour, yet the impression scarce visible, and the poison communicated not ponderable; we cannot as impossible reject this way of destruction; or deny the power of death in so narrow a circumscription.