2008 brought disappointing news. Only one caterpillar was counted. In 2009 there were none.
What could have accounted for this? 2007 was the fourth driest spring since 1895! In all probability the host plants dried up before the new caterpillars were large enough to enter diapause, the dormant stage in which they spend the hot, dry summer.
The biologists re-thought their approach, and came up with an improved plan.