If we don't count much later Sunday topper strips, Dirks can be credited with a mere two other series besides the Katzies. One was a run of the mill jungle animal strip that we'll cover one of these days, and the other is this oddball item, The Pinochle Twins. I say it's oddball because I can think of very few instances where a cartoonist ripped off his own strip with a copycat. But yet here we are with another pair of little German hellions who play tricks on their elders.
Dirks produced this strip for the Philadelphia Inquirer starting on September 16 1900, the only instance of him working for a newspaper outside of New York. It's hard to gauge when he left it, because after a few scant months he or someone else was signing the feature as Hirts, Dirts, etc. Whether this was still Dirks seeking a little plausible deniability or not I don't know. But on January 13 1901 Clare Victor "Dwig" Dwiggins officially took over the strip. Dwig kept it going, showing little interest in producing anything memorable for the feature, until September 15 of that year. He did provide a title-billed victim for the kids, Aunt Tina. The example above comes from the era of Dwig's stewardship.
Thanks to Cole Johnson for the scan!
EDIT: Cole Johnson weighs in with better information:
The Pinochle Twins had the "Aunt Tina" character from the first episode, The Pinochle Twins Show Aunt Tina Some Stunts (9-16-00). Aunt Tina lived on as the Mama surrogate in the Fineheimer Twins in 1903. Dirks was only there for four episodes (9-16 to 10-7-00), and two 1/2-page one-shots, Rebellion in the Jungle (10-7-00), and The Education of Willie Rubberneck - He Discovers his Pup has Teeth (10-28-00).
Gus Dirks contributed gag panels and one-shots throughout 1899-1900, as well as a two-episode series, Tommy the Artist and his Wonderful Living Pictures (11-18-00) and Tommy Tumps and his Wonderful Living Pictures (11-25-00). The Pinochles took 10-14 and 21 off, returning on 10-28 with The Pinochle Twins Take Aunt Tina Automobubbling by "Dirts" (Dwiggins). Following episodes were 'signed' by Squirts, Hirts, Birks, Tirks, Kirks, Lirks, Zirks, Wirks, and Girts, until 1-13-01, when Dwiggins started owning up to it. It's like they were angry with Dirks, and wanted to mock his name. Of course, September 1900 was also the same month as the weird one-shot which appeared in the Pulitzer section. He must have been playing hardball with Hearst for additional remuneration, or something.