Labelled “the pond of death” by local residents, testing showed that the body of water shared a similar purity to other ponds across the city. So what was happening to the toads? Frank Mutschmann, a veterinarian in Berlin, investigated this bizarre event and created a hypothesis: it was happening because of crows.
Toads excrete a toxic steroid called bufagin onto the skin as a defence mechanism. This can hurt predators however, crows smartly figured out a way around this. Mutschmann analysed that crows would peck into the toad's back between its chest and abdominal cavity, allowing it to extract the liver. The swift precision of the crow's attack prevented it from being exposed to the toad's secretion.
It is only after losing its liver that the toad registers the attack and subsequent removal of its liver. Their response is to inflate as a secondary line of defence. A toad has no diaphragm or ribcage and without its liver, the internal organs can expand freely. Because of the hole left in its back by the crow, the toad's lungs are expelled through the gap along with its other internal organs. Following this, the blood vessels of the toad would burst, explaining the explosive bloodshed noted by witnesses.
Mimicry enabled the crows to continue the massacre, resulting in over 1,000 toads succumbing to this peculiar demise. Something initially reminiscent of body horror from the minds of Carpenter or Cronenberg can be easily explained with some straightforward flaws evolutionary biology.
Cases of exploding toads are not isolated, with some of the first observations recorded in 1968. Outside of Hamburg, cases have been documented in Denmark and the US but the Toadpocalypse of Hamburg remains the bloodiest and most unusual.