The branches of Spruce Fir here began to show that appearance to which Clusius, if my memory does not deceive me, has
given the name of Pinus nodosa. These knots consist of innumerable little plates, looking as if all the buds had been cut short, and platted together. In the inside is lodged a great mass of very small oblong insects, or rather eggs.
June 17.
Although I walked about a good deal, and was not inattentive to what came in my way, I met with nothing peculiarly worthy of notice. On the grass I frequently observed that substance like saliva, which the common people call Frog-spittle, and which envelops a little pale flesh-coloured insect like a small Grasshopper. This insect, though not arrived at maturity, moved in some degree, and showed sufficient signs of the family to which it belonged, though it was not yet old enough to cut capers. I removed the frothy moisture from some of these insects, and on returning to them in the course of an hour, I found them covered as before; a proof
of the origin of the froth, which is produced by the animal for the purpose of protecting its tender skin against the violent heat of the sun.
Whilst I was busied in these observations, a number of cattle came running over the fields with the greatest velocity. Even the most miserably lean cows, which one would think scarcely able to drag one leg after another, went skipping along like does. Hic pauper cornua sumit[46]. They twisted their tails round and round, and went bounding and frisking about, till they at length reached a puddle, where they stopped all at once, as having found a sure asylum against the enemy that had put them to flight. Anxious to investigate what it could be that excited such extraordinary agitation, and prompted such exertions as neither the whip nor the fear of immediate death could occasion, I discovered it to be an insect which I had already
met with lower down in the country, and which is no other than an Oestrus or Gad-fly, (Asilus crabroniformis). Our Natural Historians confound the Oestrus with the Tabanus, which are as distinct from each other as a hare from a bear[47]. Cattle indeed are as much incommoded by the Broms (Tabanus bovinus) as by the very worst of the Fly or Musca tribe, to which the Tabanus certainly belongs; but by the Oestrus (Asilus) they are frightened out of
their wits. This insect does not fix itself on the body of the animal, but on the feet, between the larger and smaller hoofs. As it scarcely ever flies higher above the earth than two or three spans, and in general not more than four or five inches, the cattle, when aware of it, run as fast as they can till they get their feet into water or marshy ground, in which situations they are free from danger. The habit of the insect is that of an Ichneumon, and it much resembles a Hornet, being of a yellowish colour, with a small sharp point at its tail curved forwards. See the figure and description of Frisch, and my own specimen.
[46] "Here the poor takes up horns." Alluding to Horace's "addis cornua pauperi."
[47] By this comparison, and the subsequent allusion to an Ichneumon and a Hornet, Linnæus at the present period appears to have taken this Asilus for one of the hymenopterous order, and he even calls it an Ichneumon in Act. Upsal. ann. 1736, p. 29, n. 8. The history of its attacking the feet of cattle is given in the first edition of Fauna Suecica, 308, on the authority of the country people, but is omitted in the second, probably because Linnæus found he had been misinformed. My learned entomological friend the Rev. Mr. Kirby observes that the real Oestrus Bovis is, as has from all antiquity been believed, the cause of the above-described agitation in cattle, who escape it by running into cool damp places, which it dislikes to frequent.