Fig. 4

Thermal images of larval Necrodes littoralis warming up in the feeding matrix. Images demonstrate that heat of the larvae is a function of the matrix heat. Larvae present on the matrix may be classified into: ‘warming’ (↑) and ‘warmed’ (~). Temperature of the ‘warming’ larvae is much lower than temperature of the matrix in their vicinity and temperature of the ‘warmed’ larvae is the same or only slightly lower. There is a clear heat gradient from the outside to the inside in the ‘warming’ larvae, which indicates they are warming up in the matrix. There are also ‘cooling’ (↓) larvae, with higher body temperature than in their vicinity and a heat gradient from the inside to the outside. However, they are present only outside of the matrix. Assuming that larvae contribute endothermically to the heat of the matrix, the ‘cooling’ larvae should be present on the surface covered with the matrix. As this is not the case, the images demonstrate that heat is not endothermically generated by the larvae, but is produced in the matrix. Moreover, larvae are warming up while staying on the matrix. Because larvae frequently move through the matrix and change their position in relation to the hot spots, they take advantage of the average heat of the matrix and usually they do not reach the maximum temperatures of the matrix