Brimstones are one of the earliest butterflies in the year to appear, having over-wintered as adults by hibernating in ivy. The earliest date of emergence recorded at Howbery Park is 15 January, in 1998. More usually, they emerge whenever the first warm day in March occurs. The yellow male emerges earlier than the pale green female. They are seen flying during March, mainly with the other three hibernators (see separate page), and continue to be seen throughout the year. The latest recorded date at Howbery Park is 14 October, in 1999. They can be seen all over the site, and their numbers appear to be holding fairly steady.

The Orange Tip is often the first non-hibernator to appear. The males, with their orange-tipped wings appear earlier and are more conspicuous than the females, which lack the orange markings. They lay their conspicuous orange eggs on garlic mustard, which is common around the site, although it has become less widespread recently. Orange Tip numbers have decreased from 15 seen in 1997 to only 3 in 1999, but it is unclear if this is related to the garlic mustard or is just a natural variation (numbers in 2000 so far seem good). They are typically seen from the beginning of April to mid-June, and occur most commonly in damper areas, particularly near the river.