Welcome to "Fly Insider," The Fly's weekly recap of notable insider stock transactions.

NOTABLE INSIDER PURCHASES: Significant insider purchases reported in the prior week from December 14 through December 18 include:

•  Director of Net 1 UEPS Technologies (UEPS) Anthony Ball purchased 108,104 shares of company stock at $3.48 per share for a total transaction value of $376,105

• Beneficial owner of PDL BioPharma (PDLI) Silver Point purchased 1,748,000 shares of company stock at $2.59 per share for a total transaction value of $4,521,726

• VP of Grid Dynamics Holdings (GDYN) Victoria Livshitz purchased 126,000 shares of company stock at $11.72 per share for a total transaction value of 1,476,594

• Shareholder of Usio (USIO) Topline Capital purchased 270,389 shares of company stock at $2.03 per share for a total transaction value of $548,944

• Beneficial owner of MedAvail Holdings (MDVL) ABG WTT-MedAvail purchased 43,383 shares of company stock at $13.13 per share for a total transaction value of $569,515.

NOTABLE INSIDER SALES: Significant insider sales in the prior week from December 14 through December 18 include:

• Director of Walmart (WMT) Robson Walmart sold 1,497,151 shares of company stock at $145.93 per share for a total transaction value of $218,482,389

• Beneficial owner of GrafTech International (EAF) BCP GP sold 580,731 shares of company stock at $9.73 per share for a total transaction value of $5,651,093

• Beneficial owner of Fiserv (FISV) New Omaha Holdings sold 20,125,000 shares of company stock at $110.04 per share for a total transaction value of $2,214,555,000

• Chairman of Virgin Galactic Holdings (SPCE) Chamath Palihapitiya sold 3,800,000 shares of company stock at $25.74 per share for a total transaction value of $97,826,440

• Officer of Airbnb (ABNB) Joseph Gebbia sold 441,177 hares of company stock at $68.00 per share for a total transaction value of $30,000,036.

NOTABLE PRICE MOVEMENT AFTER INSIDER TRANSACTION: Shares of Net 1 UEPS Technologies are up approximately 29% since director Anthony Ball purchased 108,104 shares of company stock, while shares of GrafTech International are down 14% since Beneficial owner BCP GP sold 580,731 shares of company stock.