Fig. 4. The oldest female fossil mosquito (Culiseta species, 46 million years old) from the middle Eocene Kishenehn Formation in northwest Montana with blood in its abdomen. Heme (10) was identified in the abdomen by time-of-flight secondary-ion mass spectrometry and elemental analysis using energy-dispersive X-ray spectroscopy. Scale bar: 5 mm. Image reproduced with permission from D. E. Greenwalt.²⁸.